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| Features * High Performance, Low Power AVR(R) 8-Bit Microcontroller * Advanced RISC Architecture - 123 Powerful Instructions - Most Single Clock Cycle Execution - 32 x 8 General Purpose Working Registers - Fully Static Operation Non-volatile Program and Data Memories - 2/4/8K Byte of In-System Programmable Program Memory Flash (ATtiny261/461/861) Endurance: 10,000 Write/Erase Cycles - 128/256/512 Bytes In-System Programmable EEPROM (ATtiny261/461/861) Endurance: 100,000 Write/Erase Cycles - 128/256/512 Bytes Internal SRAM (ATtiny261/461/861) - Programming Lock for Self-Programming Flash Program and EEPROM Data Security Peripheral Features - 8/16-bit Timer/Counter with Prescaler - 8/10-bit High Speed Timer/Counter with Separate Prescaler 3 High Frequency PWM Outputs with Separate Output Compare Registers Programmable Dead Time Generator - Universal Serial Interface with Start Condition Detector - 10-bit ADC 11 Single Ended Channels 16 Differential ADC Channel Pairs 15 Differential ADC Channel Pairs with Programmable Gain (1x, 8x, 20x, 32x) - Programmable Watchdog Timer with Separate On-chip Oscillator - On-chip Analog Comparator Special Microcontroller Features - debugWIRE On-chip Debug System - In-System Programmable via SPI Port - External and Internal Interrupt Sources - Low Power Idle, ADC Noise Reduction, and Power-down Modes - Enhanced Power-on Reset Circuit - Programmable Brown-out Detection Circuit - Internal Calibrated Oscillator I/O and Packages - 16 Programmable I/O Lines - 20-pin SOIC, 32-pad MLF and 20-lead TSSOP Operating Voltage: - 2.7 - 5.5V for ATtiny261/461/861 Speed Grade: - ATtiny261/461/861: 0 - 8 MHz @ 2.7 - 5.5V, 0 - 16 MHz @ 4.5 - 5.5V - Operating temperature: Automotive (-40C to +125C) Low Power Consumption - Active Mode ATD On: 1 MHz, 2.7V, 25C: 300 A - Power-down Mode no Watchdog: 2.7V, 25C: 0.12 A * * 8-bit Microcontroller with 2/4/8K Bytes In-System Programmable Flash ATtiny261 ATtiny461 ATtiny861 Automotive * * * * * 7753C-AVR-07/09 1. Pin Configurations Figure 1-1. Pinout ATtiny261/461/861 SOIC / TSSOP (MOSI/DI/SDA/OC1A/PCINT8) PB0 (MISO/DO/OC1A/PCINT9) PB1 (SCK/USCK/SCL/OC1B/PCINT10) PB2 (OC1B/PCINT11) PB3 VCC GND (ADC7/OC1D/CLKI/XTAL1/PCINT12) PB4 (ADC8/OC1D/CLKO/XTAL2/PCINT13) PB5 (ADC9/INT0/T0/PCINT14) PB6 (ADC10/RESET/PCINT15) PB7 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 PA0 (ADC0/DI/SDA/PCINT0) PA1 (ADC1/DO/PCINT1) PA2 (ADC2/INT1/USCK/SCL/PCINT2) PA3 (AREF/PCINT3) AGND AVCC PA4 (ADC3/ICP0/PCINT4) PA5 (ADC4/AIN2/PCINT5) PA6 (ADC5/AIN0/PCINT6) PA7 (ADC6/AIN1/PCINT7) 32 31 30 29 28 27 26 25 PB2 (SCK/USCK/SCL/OC1B/PCINT10) PB1 (MISO/DO/OC1A/PCINT9) PB0 (MOSI/DI/SDA/OC1A/PCINT8) NC NC NC PA0 (ADC0/DI/SDA/PCINT0) PA1 (ADC1/DO/PCINT1) NC (OC1B/PCINT11) PB3 NC VCC GND NC (ADC7/OC1D/CLKI/XTAL1/PCINT12) PB4 (ADC8/OC1D/CLKO/XTAL2/PCINT13) PB5 1 2 3 4 5 6 7 8 QFN/MLF 24 23 22 21 20 19 18 17 NC PA2 (ADC2/INT1/USCK/SCL/PCINT2) PA3 (AREF/PCINT3) AGND NC NC AVCC PA4 (ADC3/ICP0/PCINT4) Note: The large center pad underneath the QFN/MLF package should be soldered to ground on the board to ensure good mechanical stability. 2 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 NC (ADC9/INT0/T0/PCINT14) PB6 (ADC10/RESET/PCINT15) PB7 NC (ADC6/AIN1/PCINT7) PA7 (ADC5/AIN0/PCINT6) PA6 (ADC4/AIN2/PCINT5) PA5 NC 9 10 11 12 13 14 15 16 ATtiny261/ATtiny461/ATtiny861 1.1 Disclaimer Typical values contained in this data sheet are based on simulations and characterization of other AVR microcontrollers manufactured on the same process technology. Min and Max values will be available after the device is characterized. 1.2 Automotive Quality Grade The ATtiny261/461/861 have been developed and manufactured according to the most stringent requirements of the international standard ISO-TS 16949. This data sheet contains limit values extracted from the results of extensive characterization (Temperature and Voltage). The quality and reliability of the ATtiny261/461/861 have been verified during regular product qualification as per AEC-Q100 grade 1. As indicated in the ordering information paragraph, the product is available in only one temperature grade, Table 1-1. Table 1-1. Temperature Grade Identification for Automotive Products Temperature Identifier Z Comments Full Automotive Temperature Range Temperature -40; +125 3 7753C-AVR-07/09 2. Overview The ATtiny261/461/861 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the ATtiny261/461/861 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed. 2.1 Block Diagram Figure 2-1. Block Diagram GND VCC Watchdog Timer Watchdog Oscillator Power Supervision POR / BOD & RESET debugWIRE PROGRAM LOGIC Oscillator Circuits / Clock Generation Flash SRAM CPU EEPROM AVCC AGND AREF Timer/Counter0 DATABUS Timer/Counter1 A/D Conv. USI Analog Comp. Internal Bandgap 3 11 PORT B (8) PORT A (8) RESET XTAL[1..2] PB[0..7] PA[0..7] The AVR core combines a rich instruction set with 32 general purpose working registers. All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be accessed in one single instruction executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs up to ten times faster than conventional CISC microcontrollers. 4 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 The ATtiny261/461/861 provides the following features: 2/4/8K byte of In-System Programmable Flash, 128/256/512 bytes EEPROM, 128/256/512 bytes SRAM, 6 general purpose I/O lines, 32 general purpose working registers, one 8-bit Timer/Counter with compare modes, one 8-bit high speed Timer/Counter, Universal Serial Interface, Internal and External Interrupts, a 4-channel, 10-bit ADC, a programmable Watchdog Timer with internal Oscillator, and three software selectable power saving modes. The Idle mode stops the CPU while allowing the SRAM, Timer/Counter, ADC, Analog Comparator, and Interrupt system to continue functioning. The Power-down mode saves the register contents, disabling all chip functions until the next Interrupt or Hardware Reset. The ADC Noise Reduction mode stops the CPU and all I/O modules except ADC, to minimize switching noise during ADC conversions. The device is manufactured using Atmel(R)'s high density non-volatile memory technology. The On-chip ISP Flash allows the Program memory to be re-programmed In-System through an SPI serial interface, by a conventional non-volatile memory programmer or by an On-chip boot code running on the AVR core. The ATtiny261/461/861 AVR is supported with a full suite of program and system development tools including: C Compilers, Macro Assemblers, Program Debugger/Simulators, In-Circuit Emulators, and Evaluation kits. 2.2 2.2.1 Pin Descriptions VCC Supply voltage. 2.2.2 GND Ground. 2.2.3 AVCC Analog supply voltage. 2.2.4 AGND Analog ground. 2.2.5 Port A (PA7..PA0) Port A is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port A output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port A pins that are externally pulled low will source current if the pull-up resistors are activated. The Port A pins are tri-stated when a reset condition becomes active, even if the clock is not running. Port A also serves the functions of various special features of the ATtiny261/461/861 as listed on page 66. 5 7753C-AVR-07/09 2.2.6 Port B (PB7..PB0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port B output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up resistors are activated. The Port B pins are tri-stated when a reset condition becomes active, even if the clock is not running. Port B also serves the functions of various special features of the ATtiny261/461/861 as listed on page 63. 2.2.7 RESET Reset input. A low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock is not running. The minimum pulse length is given in Table 23-3 on page 190. Shorter pulses are not guaranteed to generate a reset. 6 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 3. Resources A comprehensive set of development tools, application notes and datasheets are available for download on http://www.atmel.com/avr. 7 7753C-AVR-07/09 4. About Code Examples This documentation contains simple code examples that briefly show how to use various parts of the device. These code examples assume that the part specific header file is included before compilation. Be aware that not all C compiler vendors include bit definitions in the header files and interrupt handling in C is compiler dependent. Please confirm with the C compiler documentation for more details. 8 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 5. AVR CPU Core 5.1 Overview This section discusses the AVR core architecture in general. The main function of the CPU core is to ensure correct program execution. The CPU must therefore be able to access memories, perform calculations, control peripherals, and handle interrupts. Figure 5-1. Block Diagram of the AVR Architecture Data Bus 8-bit Flash Program Memory Program Counter Status and Control Instruction Register 32 x 8 General Purpose Registrers Interrupt Unit Watchdog Timer Indirect Addressing Instruction Decoder Direct Addressing ALU Control Lines Analog Comparator I/O Module1 Data SRAM I/O Module 2 I/O Module n EEPROM I/O Lines In order to maximize performance and parallelism, the AVR uses a Harvard architecture - with separate memories and buses for program and data. Instructions in the Program memory are executed with a single level pipelining. While one instruction is being executed, the next instruction is pre-fetched from the Program memory. This concept enables instructions to be executed in every clock cycle. The Program memory is In-System Reprogrammable Flash memory. 9 7753C-AVR-07/09 The fast-access Register File contains 32 x 8-bit general purpose working registers with a single clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typical ALU operation, two operands are output from the Register File, the operation is executed, and the result is stored back in the Register File - in one clock cycle. Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data Space addressing - enabling efficient address calculations. One of the these address pointers can also be used as an address pointer for look up tables in Flash Program memory. These added function registers are the 16-bit X-, Y-, and Z-register, described later in this section. The ALU supports arithmetic and logic operations between registers or between a constant and a register. Single register operations can also be executed in the ALU. After an arithmetic operation, the Status Register is updated to reflect information about the result of the operation. Program flow is provided by conditional and unconditional jump and call instructions, able to directly address the whole address space. Most AVR instructions have a single 16-bit word format. Most AVR instructions are 16-bit wide. There are also 32-bit instructions. During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack size is only limited by the total SRAM size and the usage of the SRAM. All user programs must initialize the SP in the Reset routine (before subroutines or interrupts are executed). The Stack Pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed through the five different addressing modes supported in the AVR architecture. The memory spaces in the AVR architecture are all linear and regular memory maps. A flexible interrupt module has its control registers in the I/O space with an additional Global Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector position. The lower the Interrupt Vector address, the higher the priority. The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers, SPI, and other I/O functions. The I/O memory can be accessed directly, or as the Data Space locations following those of the Register File, 0x20 - 0x5F. 5.2 ALU - Arithmetic Logic Unit The high-performance AVR ALU operates in direct connection with all the 32 general purpose working registers. Within a single clock cycle, arithmetic operations between general purpose registers or between a register and an immediate are executed. The ALU operations are divided into three main categories - arithmetic, logical, and bit-functions. Some implementations of the architecture also provide a powerful multiplier supporting both signed/unsigned multiplication and fractional format. See the "Instruction Set" section for a detailed description. 10 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 5.3 Status Register The Status Register contains information about the result of the most recently executed arithmetic instruction. This information can be used for altering program flow in order to perform conditional operations. Note that the Status Register is updated after all ALU operations, as specified in the Instruction Set Reference. This will in many cases remove the need for using the dedicated compare instructions, resulting in faster and more compact code. The Status Register is not automatically stored when entering an interrupt routine and restored when returning from an interrupt. This must be handled by software. 5.3.1 SREG - AVR Status Register The AVR Status Register - SREG - is defined as: Bit 0x3F (0x5F) Read/Write Initial Value 7 I R/W 0 6 T R/W 0 5 H R/W 0 4 S R/W 0 3 V R/W 0 2 N R/W 0 1 Z R/W 0 0 C R/W 0 SREG * Bit 7 - I: Global Interrupt Enable The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual interrupt enable control is then performed in separate control registers. If the Global Interrupt Enable Register is cleared, none of the interrupts are enabled independent of the individual interrupt enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by the application with the SEI and CLI instructions, as described in the instruction set reference. * Bit 6 - T: Bit Copy Storage The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination for the operated bit. A bit from a register in the Register File can be copied into T by the BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the BLD instruction. * Bit 5 - H: Half Carry Flag The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry is useful in BCD arithmetic. See the "Instruction Set Description" for detailed information. * Bit 4 - S: Sign Bit, S = N V The S-bit is always an exclusive or between the Negative Flag N and the Two's Complement Overflow Flag V. See the "Instruction Set Description" for detailed information. * Bit 3 - V: Two's Complement Overflow Flag The Two's Complement Overflow Flag V supports two's complement arithmetics. See the "Instruction Set Description" for detailed information. * Bit 2 - N: Negative Flag The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the "Instruction Set Description" for detailed information. 11 7753C-AVR-07/09 * Bit 1 - Z: Zero Flag The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the "Instruction Set Description" for detailed information. * Bit 0 - C: Carry Flag The Carry Flag C indicates a carry in an arithmetic or logic operation. See the "Instruction Set Description" for detailed information. 5.4 General Purpose Register File The Register File is optimized for the AVR Enhanced RISC instruction set. In order to achieve the required performance and flexibility, the following input/output schemes are supported by the Register File: * One 8-bit output operand and one 8-bit result input * Two 8-bit output operands and one 8-bit result input * Two 8-bit output operands and one 16-bit result input * One 16-bit output operand and one 16-bit result input Figure 5-2 shows the structure of the 32 general purpose working registers in the CPU. Figure 5-2. AVR CPU General Purpose Working Registers 7 R0 R1 R2 ... R13 General Purpose Working Registers R14 R15 R16 R17 ... R26 R27 R28 R29 R30 R31 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F X-register Low Byte X-register High Byte Y-register Low Byte Y-register High Byte Z-register Low Byte Z-register High Byte 0x0D 0x0E 0x0F 0x10 0x11 0 Addr. 0x00 0x01 0x02 Most of the instructions operating on the Register File have direct access to all registers, and most of them are single cycle instructions. As shown in Figure 5-2, each register is also assigned a Data memory address, mapping them directly into the first 32 locations of the user Data Space. Although not being physically implemented as SRAM locations, this memory organization provides great flexibility in access of the registers, as the X-, Y- and Z-pointer registers can be set to index any register in the file. 12 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 5.4.1 The X-register, Y-register, and Z-register The registers R26..R31 have some added functions to their general purpose usage. These registers are 16-bit address pointers for indirect addressing of the data space. The three indirect address registers X, Y, and Z are defined as described in Figure 5-3 on page 13. Figure 5-3. The X-, Y-, and Z-registers 15 X-register 7 R27 (0x1B) XH 0 7 R26 (0x1A) XL 0 0 15 Y-register 7 R29 (0x1D) 15 Z-register 7 R31 (0x1F) YH 0 7 R28 (0x1C) ZH 0 7 R30 (0x1E) YL 0 0 ZL 0 0 In the different addressing modes these address registers have functions as fixed displacement, automatic increment, and automatic decrement (see the instruction set reference for details). 5.5 Stack Pointer The Stack is mainly used for storing temporary data, for storing local variables and for storing return addresses after interrupts and subroutine calls. The Stack Pointer Register always points to the top of the Stack. Note that the Stack is implemented as growing from higher memory locations to lower memory locations. This implies that a Stack PUSH command decreases the Stack Pointer. The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt Stacks are located. This Stack space in the data SRAM must be defined by the program before any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set to point above 0x60. The Stack Pointer is decremented by one when data is pushed onto the Stack with the PUSH instruction, and it is decremented by two when the return address is pushed onto the Stack with subroutine call or interrupt. The Stack Pointer is incremented by one when data is popped from the Stack with the POP instruction, and it is incremented by two when data is popped from the Stack with return from subroutine RET or return from interrupt RETI. The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of bits actually used is implementation dependent. Note that the data space in some implementations of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register will not be present 13 7753C-AVR-07/09 5.5.1 SPH and SPL - Stack Pointer Register Bit 0x3E (0x5E) 0x3D (0x5D) 15 SP15 SP7 7 Read/Write R/W R/W Initial Value RAMEND RAMEND 14 SP14 SP6 6 R/W R/W RAMEND RAMEND 13 SP13 SP5 5 R/W R/W RAMEND RAMEND 12 SP12 SP4 4 R/W R/W RAMEND RAMEND 11 SP11 SP3 3 R/W R/W RAMEND RAMEND 10 SP10 SP2 2 R/W R/W RAMEND RAMEND 9 SP9 SP1 1 R/W R/W RAMEND RAMEND 8 SP8 SP0 0 R/W R/W RAMEND RAMEND SPH SPL 5.6 Instruction Execution Timing This section describes the general access timing concepts for instruction execution. The AVR CPU is driven by the CPU clock clkCPU, directly generated from the selected clock source for the chip. No internal clock division is used. Figure 5-4 shows the parallel instruction fetches and instruction executions enabled by the Harvard architecture and the fast access Register File concept. This is the basic pipelining concept to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost, functions per clocks, and functions per power-unit. Figure 5-4. The Parallel Instruction Fetches and Instruction Executions T1 T2 T3 T4 clkCPU 1st Instruction Fetch 1st Instruction Execute 2nd Instruction Fetch 2nd Instruction Execute 3rd Instruction Fetch 3rd Instruction Execute 4th Instruction Fetch Figure 5-5 shows the internal timing concept for the Register File. In a single clock cycle an ALU operation using two register operands is executed, and the result is stored back to the destination register. Figure 5-5. Single Cycle ALU Operation T1 T2 T3 T4 clkCPU Total Execution Time Register Operands Fetch ALU Operation Execute Result Write Back 14 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 5.7 Reset and Interrupt Handling The AVR provides several different interrupt sources. These interrupts and the separate Reset Vector each have a separate Program Vector in the Program memory space. All interrupts are assigned individual enable bits which must be written logic one together with the Global Interrupt Enable bit in the Status Register in order to enable the interrupt. The lowest addresses in the Program memory space are by default defined as the Reset and Interrupt Vectors. The complete list of vectors is shown in "Interrupts" on page 50. The list also determines the priority levels of the different interrupts. The lower the address the higher is the priority level. RESET has the highest priority, and next is INT0 - the External Interrupt Request 0. When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are disabled. The user software can write logic one to the I-bit to enable nested interrupts. All enabled interrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a Return from Interrupt instruction - RETI - is executed. There are basically two types of interrupts. The first type is triggered by an event that sets the Interrupt Flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vector in order to execute the interrupt handling routine, and hardware clears the corresponding Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit position(s) to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is cleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag is cleared by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt Enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the Global Interrupt Enable bit is set, and will then be executed by order of priority. The second type of interrupts will trigger as long as the interrupt condition is present. These interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before the interrupt is enabled, the interrupt will not be triggered. When the AVR exits from an interrupt, it will always return to the main program and execute one more instruction before any pending interrupt is served. Note that the Status Register is not automatically stored when entering an interrupt routine, nor restored when returning from an interrupt routine. This must be handled by software. When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled. No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the CLI instruction. The following example shows how this can be used to avoid interrupts during the timed EEPROM write sequence. 15 7753C-AVR-07/09 Assembly Code Example in r16, SREG cli sbi EECR, EEMPE sbi EECR, EEPE out SREG, r16 ; restore SREG value (I-bit) ; store SREG value ; start EEPROM write ; disable interrupts during timed sequence C Code Example char cSREG; cSREG = SREG; /* store SREG value */ /* disable interrupts during timed sequence */ _CLI(); EECR |= (1< sei ; set Global Interrupt Enable sleep; enter sleep, waiting for interrupt ; note: will enter sleep before any pending ; interrupt(s) C Code Example _SEI(); /* set Global Interrupt Enable */ _SLEEP(); /* enter sleep, waiting for interrupt */ /* note: will enter sleep before any pending interrupt(s) */ 5.7.1 Interrupt Response Time The interrupt execution response for all the enabled AVR interrupts is four clock cycles minimum. After four clock cycles the Program Vector address for the actual interrupt handling routine is executed. During this four clock cycle period, the Program Counter is pushed onto the Stack. The vector is normally a jump to the interrupt routine, and this jump takes three clock cycles. If an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed before the interrupt is served. If an interrupt occurs when the MCU is in sleep mode, the interrupt execution response time is increased by four clock cycles. This increase comes in addition to the start-up time from the selected sleep mode. A return from an interrupt handling routine takes four clock cycles. During these four clock cycles, the Program Counter (two bytes) is popped back from the Stack, the Stack Pointer is incremented by two, and the I-bit in SREG is set. 16 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 6. AVR Memories This section describes the different memories in the ATtiny261/461/861. The AVR architecture has two main memory spaces, the Data memory and the Program memory space. In addition, the ATtiny261/461/861 features an EEPROM Memory for data storage. All three memory spaces are linear and regular. 6.1 In-System Re-programmable Flash Program Memory The ATtiny261/461/861 contains 2/4/8K byte On-chip In-System Reprogrammable Flash memory for program storage. Since all AVR instructions are 16 or 32 bits wide, the Flash is organized as 1024/2048/4096 x 16. The Flash memory has an endurance of at least 10,000 write/erase cycles. The ATtiny261/461/861 Program Counter (PC) is 10/11/12 bits wide, thus addressing the 1024/2048/4096 Program memory locations. "Memory Programming" on page 171 contains a detailed description on Flash data serial downloading using the SPI pins. Constant tables can be allocated within the entire Program memory address space (see the LPM - Load Program memory instruction description). Timing diagrams for instruction fetch and execution are presented in "Instruction Execution Timing" on page 14. Figure 6-1. Program Memory Map Program Memory 0x0000 0x03FF/0x07FF/0x0FFF 6.2 SRAM Data Memory Figure 6-2 shows how the ATtiny261/461/861 SRAM Memory is organized. The lower 224/352/608 Data memory locations address both the Register File, the I/O memory and the internal data SRAM. The first 32 locations address the Register File, the next 64 locations the standard I/O memory, and the last 128/256/512 locations address the internal data SRAM. The five different addressing modes for the Data memory cover: Direct, Indirect with Displacement, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In the Register File, registers R26 to R31 feature the indirect addressing pointer registers. The direct addressing reaches the entire data space. The Indirect with Displacement mode reaches 63 address locations from the base address given by the Y- or Z-register. 17 7753C-AVR-07/09 When using register indirect addressing modes with automatic pre-decrement and post-increment, the address registers X, Y, and Z are decremented or incremented. The 32 general purpose working registers, 64 I/O Registers, and the 128/256/512 bytes of internal data SRAM in the ATtiny261/461/861 are all accessible through all these addressing modes. The Register File is described in "General Purpose Register File" on page 12. Figure 6-2. Data Memory Map Data Memory 32 Registers 64 I/O Registers 0x0000 - 0x001F 0x0020 - 0x005F 0x0060 Internal SRAM (128/256/512 x 8) 0x0DF/0x15F/0x25F 6.2.1 Data Memory Access Times This section describes the general access timing concepts for internal memory access. The internal data SRAM access is performed in two clkCPU cycles as described in Figure 6-3. Figure 6-3. On-chip Data SRAM Access Cycles T1 T2 T3 clkCPU Address Data WR Data RD Compute Address Address valid Memory Access Instruction Next Instruction 6.3 EEPROM Data Memory The ATtiny261/461/861 contains 128/256/512 bytes of data EEPROM memory. It is organized as a separate data space, in which single bytes can be read and written. The EEPROM has an endurance of at least 100,000 write/erase cycles. The access between the EEPROM and the CPU is described in the following, specifying the EEPROM Address Registers, the EEPROM Data Register, and the EEPROM Control Register. For a detailed description of Serial data downloading to the EEPROM, see page 183. 18 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 Read Write ATtiny261/ATtiny461/ATtiny861 6.3.1 EEPROM Read/Write Access The EEPROM Access Registers are accessible in the I/O space. The write access times for the EEPROM are given in Table 6-1. A self-timing function, however, lets the user software detect when the next byte can be written. If the user code contains instructions that write the EEPROM, some precautions must be taken. In heavily filtered power supplies, VCC is likely to rise or fall slowly on Power-up/down. This causes the device for some period of time to run at a voltage lower than specified as minimum for the clock frequency used. See "Preventing EEPROM Corruption" on page 21 for details on how to avoid problems in these situations. In order to prevent unintentional EEPROM writes, a specific write procedure must be followed. Refer to "Atomic Byte Programming" on page 19 and "Split Byte Programming" on page 19 for details on this. When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next instruction is executed. 6.3.2 Atomic Byte Programming Using Atomic Byte Programming is the simplest mode. When writing a byte to the EEPROM, the user must write the address into the EEARL Register and data into EEDR Register. If the EEPMn bits are zero, writing EEPE (within four cycles after EEMPE is written) will trigger the erase/write operation. Both the erase and write cycle are done in one operation and the total programming time is given in Table 1. The EEPE bit remains set until the erase and write operations are completed. While the device is busy with programming, it is not possible to do any other EEPROM operations. Split Byte Programming It is possible to split the erase and write cycle in two different operations. This may be useful if the system requires short access time for some limited period of time (typically if the power supply voltage falls). In order to take advantage of this method, it is required that the locations to be written have been erased before the write operation. But since the erase and write operations are split, it is possible to do the erase operations when the system allows doing time-critical operations (typically after Power-up). Erase To erase a byte, the address must be written to EEAR. If the EEPMn bits are 0b01, writing the EEPE (within four cycles after EEMPE is written) will trigger the erase operation only (programming time is given in Table 1). The EEPE bit remains set until the erase operation completes. While the device is busy programming, it is not possible to do any other EEPROM operations. 6.3.5 Write To write a location, the user must write the address into EEAR and the data into EEDR. If the EEPMn bits are 0b10, writing the EEPE (within four cycles after EEMPE is written) will trigger the write operation only (programming time is given in Table 1). The EEPE bit remains set until the write operation completes. If the location to be written has not been erased before write, the data that is stored must be considered as lost. While the device is busy with programming, it is not possible to do any other EEPROM operations. 6.3.3 6.3.4 19 7753C-AVR-07/09 The calibrated Oscillator is used to time the EEPROM accesses. Make sure the Oscillator frequency is within the requirements described in "OSCCAL - Oscillator Calibration Register" on page 32. The following code examples show one assembly and one C function for erase, write, or atomic write of the EEPROM. The examples assume that interrupts are controlled (e.g., by disabling interrupts globally) so that no interrupts will occur during execution of these functions. Assembly Code Example EEPROM_write: ; Wait for completion of previous write sbic EECR,EEPE rjmp EEPROM_write ; Set Programming mode ldi out r16, (0< C Code Example void EEPROM_write(unsigned char ucAddress, unsigned char ucData) { /* Wait for completion of previous write */ while(EECR & (1< ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 The next code examples show assembly and C functions for reading the EEPROM. The examples assume that interrupts are controlled so that no interrupts will occur during execution of these functions. Assembly Code Example EEPROM_read: ; Wait for completion of previous write sbic EECR,EEPE rjmp EEPROM_read ; Set up address (r18:r17) in address register out EEARH, r18 out EEARL, r17 ; Start eeprom read by writing EERE sbi EECR,EERE ; Read data from data register in ret r16,EEDR C Code Example unsigned char EEPROM_read(unsigned char ucAddress) { /* Wait for completion of previous write */ while(EECR & (1< Preventing EEPROM Corruption During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is too low for the CPU and the EEPROM to operate properly. These issues are the same as for board level systems using EEPROM, and the same design solutions should be applied. An EEPROM data corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to the EEPROM requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the supply voltage is too low. EEPROM data corruption can easily be avoided by following this design recommendation: Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can be done by enabling the internal Brown-out Detector (BOD). If the detection level of the internal BOD does not match the needed detection level, an external low VCC reset protection circuit can be used. If a reset occurs while a write operation is in progress, the write operation will be completed provided that the power supply voltage is sufficient. 21 7753C-AVR-07/09 6.4 I/O Memory The I/O space definition of the ATtiny261/461/861 is shown in "Register Summary" on page 209. All ATtiny261/461/861 I/Os and peripherals are placed in the I/O space. All I/O locations may be accessed by the LD/LDS/LDD and ST/STS/STD instructions, transferring data between the 32 general purpose working registers and the I/O space. I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the value of single bits can be checked by using the SBIS and SBIC instructions. Refer to the instruction set section for more details. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these addresses. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses should never be written. Some of the Status Flags are cleared by writing a logical one to them. Note that, the CBI and SBI instructions will only operate on the specified bit, and can therefore be used on registers containing such Status Flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only. The I/O and Peripherals Control Registers are explained in later sections. 6.4.1 General Purpose I/O Registers The ATtiny261/461/861 contains three General Purpose I/O Registers. These registers can be used for storing any information, and they are particularly useful for storing global variables and Status Flags. General Purpose I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI, CBI, SBIS, and SBIC instructions. 6.5 6.5.1 Register Description EEARH and EEARL - EEPROM Address Register Bit 0x1F (0x3F) 0x1E (0x3E) Bit Read/Write Read/Write Initial Value Initial Value 7 EEAR7 7 R R/W 0 X 6 EEAR6 6 R R/W 0 X 5 EEAR5 5 R R/W 0 X 4 EEAR4 4 R R/W 0 X 3 EEAR3 3 R R/W 0 X 2 EEAR2 2 R R/W 0 X 1 EEAR1 1 R R/W 0 X 0 EEAR8 EEAR0 0 R/W R/W X X EEARH EEARL * Bit 7:1 - Res6:0: Reserved Bits These bits are reserved for future use and will always read as 0 in ATtiny261/461/861. * Bits 8:0 - EEAR8:0: EEPROM Address The EEPROM Address Registers - EEARH and EEARL - specifies the high EEPROM address in the 128/256/512 bytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and 127/255/511. The initial value of EEAR is undefined. A proper value must be written before the EEPROM may be accessed. 22 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 6.5.2 EEDR - EEPROM Data Register Bit 0x1D (0x3D) Read/Write Initial Value 7 EEDR7 R/W 0 6 EEDR6 R/W 0 5 EEDR5 R/W 0 4 EEDR4 R/W 0 3 EEDR3 R/W 0 2 EEDR2 R/W 0 1 EEDR1 R/W 0 0 EEDR0 R/W 0 EEDR * Bits 7:0 - EEDR7:0: EEPROM Data For the EEPROM write operation the EEDR Register contains the data to be written to the EEPROM in the address given by the EEAR Register. For the EEPROM read operation, the EEDR contains the data read out from the EEPROM at the address given by EEAR. 6.5.3 EECR - EEPROM Control Register Bit 0x1C (0x3C) Read/Write Initial Value 7 - R 0 6 - R 0 5 EEPM1 R/W X 4 EEPM0 R/W X 3 EERIE R/W 0 2 EEMPE R/W 0 1 EEPE R/W X 0 EERE R/W 0 EECR * Bit 7 - Res: Reserved Bit This bit is reserved for future use and will always read as 0 in ATtiny261/461/861. For compatibility with future AVR devices, always write this bit to zero. After reading, mask out this bit. * Bit 6 - Res: Reserved Bit This bit is reserved in the ATtiny261/461/861 and will always read as zero. * Bits 5, 4 - EEPM1 and EEPM0: EEPROM Programming Mode Bits The EEPROM Programming mode bits setting defines which programming action that will be triggered when writing EEPE. It is possible to program data in one atomic operation (erase the old value and program the new value) or to split the Erase and Write operations in two different operations. The Programming times for the different modes are shown in Table 6-1. While EEPE is set, any write to EEPMn will be ignored. During reset, the EEPMn bits will be reset to 0b00 unless the EEPROM is busy programming. Table 6-1. EEPM1 0 0 1 1 EEPROM Mode Bits EEPM0 0 1 0 1 Programming Time 3.4 ms 1.8 ms 1.8 ms - Operation Erase and Write in one operation (Atomic Operation) Erase Only Write Only Reserved for future use * Bit 3 - EERIE: EEPROM Ready Interrupt Enable Writing EERIE to one enables the EEPROM Ready Interrupt if the I-bit in SREG is set. Writing EERIE to zero disables the interrupt. The EEPROM Ready Interrupt generates a constant interrupt when Non-volatile memory is ready for programming. 23 7753C-AVR-07/09 * Bit 2 - EEMPE: EEPROM Master Program Enable The EEMPE bit determines whether writing EEPE to one will have effect or not. When EEMPE is set, setting EEPE within four clock cycles will program the EEPROM at the selected address. If EEMPE is zero, setting EEPE will have no effect. When EEMPE has been written to one by software, hardware clears the bit to zero after four clock cycles. * Bit 1 - EEPE: EEPROM Program Enable The EEPROM Program Enable Signal EEPE is the programming enable signal to the EEPROM. When EEPE is written, the EEPROM will be programmed according to the EEPMn bits setting. The EEMPE bit must be written to one before a logical one is written to EEPE, otherwise no EEPROM write takes place. When the write access time has elapsed, the EEPE bit is cleared by hardware. When EEPE has been set, the CPU is halted for two cycles before the next instruction is executed. * Bit 0 - EERE: EEPROM Read Enable The EEPROM Read Enable Signal - EERE - is the read strobe to the EEPROM. When the correct address is set up in the EEAR Register, the EERE bit must be written to one to trigger the EEPROM read. The EEPROM read access takes one instruction, and the requested data is available immediately. When the EEPROM is read, the CPU is halted for four cycles before the next instruction is executed. The user should poll the EEPE bit before starting the read operation. If a write operation is in progress, it is neither possible to read the EEPROM, nor to change the EEAR Register. 6.5.4 GPIOR2 - General Purpose I/O Register 2 Bit 0x0C (0x2C) Read/Write Initial Value 7 MSB R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 6 5 4 3 2 1 0 LSB R/W 0 GPIOR2 6.5.5 GPIOR1 - General Purpose I/O Register 1 Bit 0x0B (0x2B) Read/Write Initial Value 7 MSB R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 6 5 4 3 2 1 0 LSB R/W 0 GPIOR1 6.5.6 GPIOR0 - General Purpose I/O Register 0 Bit 0x0A (0x2A) Read/Write Initial Value 7 MSB R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 6 5 4 3 2 1 0 LSB R/W 0 GPIOR0 24 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 7. System Clock and Clock Options 7.1 Clock Systems and their Distribution Figure 7-1 presents the principal clock systems in the AVR and their distribution. All of the clocks need not be active at a given time. In order to reduce power consumption, the clocks to modules not being used can be halted by using different sleep modes, as described in "Power Management and Sleep Modes" on page 35. The clock systems are detailed below. Figure 7-1. Clock Distribution 7.1.1 CPU Clock - clkCPU The CPU clock is routed to parts of the system concerned with operation of the AVR core. Examples of such modules are the General Purpose Register File, the Status Register and the Data memory holding the Stack Pointer. Halting the CPU clock inhibits the core from performing general operations and calculations. I/O Clock - clkI/O The I/O clock is used by the majority of the I/O modules, like Timer/Counter. The I/O clock is also used by the External Interrupt module, but note that some external interrupts are detected by asynchronous logic, allowing such interrupts to be detected even if the I/O clock is halted. Flash Clock - clkFLASH The Flash clock controls operation of the Flash interface. The Flash clock is usually active simultaneously with the CPU clock. ADC Clock - clkADC The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks in order to reduce noise generated by digital circuitry. This gives more accurate ADC conversion results. 7.1.2 7.1.3 7.1.4 25 7753C-AVR-07/09 7.1.5 Internal PLL for Fast Peripheral Clock Generation - clkPCK The internal PLL in ATtiny261/461/861 generates a clock frequency that is 8x multiplied from a source input. By default, the PLL uses the output of the internal 8.0 MHz RC oscillator as source. Alternatively, if the LSM bit of the PLLCSR is set the PLL will use the output of the RC oscillator divided by two. Thus the output of the PLL, the fast peripheral clock is 64 MHz. The fast peripheral clock, or a clock prescaled from that, can be selected as the clock source for Timer/Counter1or as a system clock. See Figure 7-2. The frequency of the fast peripheral clock is divided by two when LSM of PLLCSR is set, resulting in a clock frequency of 32 MHz. Note, that LSM can not be set if PLLCLK is used as a system clock. Figure 7-2. OSCCAL PCK Clocking System LSM PLLE CKSEL3:0 CLKPS3:0 LOCK DETECTOR 1/2 8.0 MHz OSCILLATOR PLOCK 4 MHz PCK 8 MHz PLL 8x 64 / 32 MHz 1/4 16 MHz 8 MHz PRESCALER SYSTEM CLOCK XTAL1 XTAL2 OSCILLATORS The PLL is locked on the RC oscillator and adjusting the RC oscillator via OSCCAL register will adjust the fast peripheral clock at the same time. However, even if the RC oscillator is taken to a higher frequency than 8 MHz, the fast peripheral clock frequency saturates at 85 MHz (worst case) and remains oscillating at the maximum frequency. It should be noted that the PLL in this case is not locked any longer with the RC oscillator clock. Therefore, it is recommended not to take the OSCCAL adjustments to a higher frequency than 8 MHz in order to keep the PLL in the correct operating range. The internal PLL is enabled when: * The PLLE bit of the PLLCSR register is set. * The CKSEL fuse are programmed to `0001'. The PLLCSR bit PLOCK is set when PLL is locked. Both internal RC oscillator and PLL are switched off in power down and stand-by sleep modes. 26 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 7.2 Clock Sources The device has the following clock source options, selectable by Flash Fuse bits as shown below. The clock from the selected source is input to the AVR clock generator, and routed to the appropriate modules. Table 7-1. Device Clocking Options Select(1) vs. PB4 and PB5 Functionality CKSEL3..0 0000 0001 0010 0011 01xx 1000 1001 1010 1011 1100 1101 1110 1111 PB4 XTAL1 I/O I/O I/O XTAL1 XTAL1 XTAL1 XTAL1 XTAL1 XTAL1 XTAL1 XTAL1 XTAL1 PB5 I/O I/O I/O I/O XTAL2 XTAL2 XTAL2 XTAL2 XTAL2 XTAL2 XTAL2 XTAL2 XTAL2 Device Clocking Option External Clock PLL Clock Calibrated Internal RC Oscillator 8.0 MHz Watchdog Oscillator 128 kHz External Low-Frequency Crystal External Crystal/Ceramic Resonator (0.4 - 0.9 MHz) External Crystal/Ceramic Resonator (0.4 - 0.9 MHz) External Crystal/Ceramic Resonator (0.9 - 3.0 MHz) External Crystal/Ceramic Resonator (0.9 - 3.0 MHz) External Crystal/Ceramic Resonator (3.0 - 8.0 MHz) External Crystal/Ceramic Resonator (3.0 - 8.0 MHz) External Crystal/Ceramic Resonator (8.0 - 16.0 MHz) External Crystal/Ceramic Resonator (8.0 - 16.0 MHz) Note: 1. For all fuses "1" means unprogrammed while "0" means programmed. The various choices for each clocking option is given in the following sections. When the CPU wakes up from Power-down or Power-save, the selected clock source is used to time the start-up, ensuring stable Oscillator operation before instruction execution starts. When the CPU starts from reset, there is an additional delay allowing the power to reach a stable level before commencing normal operation. The Watchdog Oscillator is used for timing this real-time part of the start-up time. The number of WDT Oscillator cycles used for each time-out is shown in Table 7-2. Table 7-2. Number of Watchdog Oscillator Cycles Typ Time-out 4 ms 64 ms Number of Cycles 512 8K (8,192) 7.3 Default Clock Source The device is shipped with CKSEL = "0010", SUT = "10", and CKDIV8 programmed. The default clock source setting is therefore the Internal RC Oscillator running at 8 MHz with longest start-up time and an initial system clock prescaling of 8. This default setting ensures that all users can make their desired clock source setting using an In-System or High-voltage Programmer. 7.4 External Clock To drive the device from an external clock source, CLKI should be driven as shown in Figure 7-3. To run the device on an external clock, the CKSEL Fuses must be programmed to "0000". 27 7753C-AVR-07/09 Figure 7-3. External Clock Drive Configuration EXTERNAL CLOCK SIGNAL CLKI GND When this clock source is selected, start-up times are determined by the SUT Fuses as shown in Table 7-3. Table 7-3. SUT1..0 00 01 10 11 Start-up Times for the External Clock Selection Start-up Time from Power-down and Power-save 6 CK 6 CK 6 CK Additional Delay from Reset 14CK 14CK + 4 ms 14CK + 64 ms Reserved Recommended Usage BOD enabled Fast rising power Slowly rising power Note that the System Clock Prescaler can be used to implement run-time changes of the internal clock frequency while still ensuring stable operation. Refer to "System Clock Prescaler" on page 32 for details. 7.5 High Frequency PLL Clock - PLLCLK There is an internal PLL that provides nominally 64 MHz clock rate locked to the RC Oscillator for the use of the Peripheral Timer/Counter1 and for the system clock source. When selected as a system clock source, by programming the CKSEL fuses to `0001', it is divided by four like shown in Table 7-4. When this clock source is selected, start-up times are determined by the SUT fuses as shown in Table 7-5. See also "PCK Clocking System" on page 26. Table 7-4. PLLCK Operating Modes CKSEL3..0 0001 Nominal Frequency 16 MHz Table 7-5. SUT1..0 00 01 10 11 Start-up Times for the PLLCK Start-up Time from Power Down 14CK + 1K (1024) + 4 ms 14CK + 16K (16384) + 4 ms 14CK + 1K (1024) + 64 ms 14CK + 16K (16384) + 64 ms Additional Delay from Power-On-Reset (VCC = 5.0V) Recommended usage 4 ms 4 ms 4 ms 4 ms BOD enabled Fast rising power Slowly rising power Slowly rising power 28 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 7.6 Calibrated Internal RC Oscillator By default, the Internal RC Oscillator provides an approximate 8.0 MHz clock. Though voltage and temperature dependent, this clock can be very accurately calibrated by the user. See Table 23-1 on page 189 and "Internal Oscillator Speed" on page 207 for more details. The device is shipped with the CKDIV8 Fuse programmed. See "System Clock Prescaler" on page 32 for more details. This clock may be selected as the system clock by programming the CKSEL Fuses as shown in Table 7-6 on page 29. If selected, it will operate with no external components. During reset, hardware loads the pre-programmed calibration value into the OSCCAL Register and thereby automatically calibrates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in Table 23-1 on page 189. By changing the OSCCAL register from SW, see "OSCCAL - Oscillator Calibration Register" on page 32, it is possible to get a higher calibration accuracy than by using the factory calibration. The accuracy of this calibration is shown as User calibration in Table 23-1 on page 189. When this Oscillator is used as the chip clock, the Watchdog Oscillator will still be used for the Watchdog Timer and for the Reset Time-out. For more information on the pre-programmed calibration value, see the section "Calibration Byte" on page 173. Table 7-6. Internal Calibrated RC Oscillator Operating Modes(1)(2) Frequency Range (MHz) 7.84 - 8.16 Notes: CKSEL3..0 0010 1. The device is shipped with this option selected. 2. If 8 MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8 Fuse can be programmed in order to divide the internal frequency by 8. When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in Table 7-7 on page 29. Table 7-7. SUT1..0 00 01 10(1) 11 Note: Start-up Times for the Internal Calibrated RC Oscillator Clock Selection Start-up Time from Power-down 6 CK 6 CK 6 CK Additional Delay from Reset (VCC = 5.0V) 14CK 14CK + 4 ms 14CK + 64 ms Reserved Recommended Usage BOD enabled Fast rising power Slowly rising power 1. The device is shipped with this option selected. 29 7753C-AVR-07/09 7.7 128 kHz Internal Oscillator The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The frequency is nominal at 3V and 25C. This clock may be select as the system clock by programming the CKSEL Fuses to "0011". When this clock source is selected, start-up times are determined by the SUT Fuses as shown in Table 7-8. Table 7-8. SUT1..0 00 01 10 11 Start-up Times for the 128 kHz Internal Oscillator Start-up Time from Power-down and Power-save 6 CK 6 CK 6 CK Additional Delay from Reset 14CK 14CK + 4 ms 14CK + 64 ms Reserved Recommended Usage BOD enabled Fast rising power Slowly rising power 7.8 Low-frequency Crystal Oscillator To use a 32.768 kHz watch crystal as the clock source for the device, the low-frequency crystal oscillator must be selected by setting CKSEL fuses to `0100'. The crystal should be connected as shown in Figure 7-4. Refer to the 32 kHz Crystal Oscillator Application Note for details on oscillator operation and how to choose appropriate values for C1 and C2. When this oscillator is selected, start-up times are determined by the SUT fuses as shown in Table 7-9. Table 7-9. SUT1..0 00 01 10 11 Notes: Start-up Times for the Low Frequency Crystal Oscillator Clock Selection Start-up Time from Power Down and Power Save 1K (1024) CK 1K (1024) CK (1) (1) Additional Delay from Reset (VCC = 5.0V) 4 ms 64 ms 64 ms Reserved Recommended usage Fast rising power or BOD enabled Slowly rising power Stable frequency at start-up 32K (32768) CK 1. These options should only be used if frequency stability at start-up is not important for the application. 7.9 Crystal Oscillator XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be configured for use as an On-chip Oscillator, as shown in Figure 7-4. Either a quartz crystal or a ceramic resonator may be used. C1 and C2 should always be equal for both crystals and resonators. The optimal value of the capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of the environment. Some initial guidelines for choosing capacitors for use with crystals are given in Table 7-10. For ceramic resonators, the capacitor values given by the manufacturer should be used. 30 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 7-4. Crystal Oscillator Connections C2 C1 XTAL2 XTAL1 GND The Oscillator can operate in three different modes, each optimized for a specific frequency range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 7-10. Table 7-10. CKSEL3..1 100(1) 101 110 111 Notes: Crystal Oscillator Operating Modes Frequency Range (MHz) 0.4 - 0.9 0.9 - 3.0 3.0 - 8.0 8.0 Recommended Range for Capacitors C1 and C2 for Use with Crystals (pF) - 12 - 22 12 - 22 12 - 22 1. This option should not be used with crystals, only with ceramic resonators. The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table 7-11. Table 7-11. Start-up Times for the Crystal Oscillator Clock Selection Start-up Time from Power-down and Power-save 258 CK(1) 258 CK(1) 1K (1024) CK(2) 1K (1024)CK(2) 1K (1024)CK(2) 16K (16384) CK 16K (16384) CK 16K (16384) CK Additional Delay from Reset (VCC = 5.0V) Recommended Usage 14CK + 4.1 ms 14CK + 65 ms 14CK 14CK + 4.1 ms 14CK + 65 ms 14CK 14CK + 4.1 ms 14CK + 65 ms Ceramic resonator, fast rising power Ceramic resonator, slowly rising power Ceramic resonator, BOD enabled Ceramic resonator, fast rising power Ceramic resonator, slowly rising power Crystal Oscillator, BOD enabled Crystal Oscillator, fast rising power Crystal Oscillator, slowly rising power CKSEL0 0 0 0 0 1 1 1 1 Notes: SUT1..0 00 01 10 11 00 01 10 11 1. These options should only be used when not operating close to the maximum frequency of the device, and only if frequency stability at start-up is not important for the application. These options are not suitable for crystals. 2. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up. They can also be used with crystals when not operating close to the maximum frequency of the device, and if frequency stability at start-up is not important for the application. 31 7753C-AVR-07/09 7.10 Clock Output Buffer The device can output the system clock on the CLKO pin. To enable the output, the CKOUT Fuse has to be programmed. This mode is suitable when the chip clock is used to drive other circuits on the system. Note that the clock will not be output during reset and the normal operation of I/O pin will be overridden when the fuse is programmed. Any clock source, including the internal RC Oscillator, can be selected when the clock is output on CLKO. If the System Clock Prescaler is used, it is the divided system clock that is output. 7.11 System Clock Prescaler The ATtiny261/461/861 system clock can be divided by setting the Clock Prescale Register - CLKPR. This feature can be used to decrease power consumption when the requirement for processing power is low. This can be used with all clock source options, and it will affect the clock frequency of the CPU and all synchronous peripherals. clkI/O, clkADC, clkCPU, and clkFLASH are divided by a factor as shown in Table 7-12. 7.11.1 Switching Time When switching between prescaler settings, the System Clock Prescaler ensures that no glitches occur in the clock system and that no intermediate frequency is higher than neither the clock frequency corresponding to the previous setting, nor the clock frequency corresponding to the new setting. The ripple counter that implements the prescaler runs at the frequency of the undivided clock, which may be faster than the CPU's clock frequency. Hence, it is not possible to determine the state of the prescaler - even if it were readable, and the exact time it takes to switch from one clock division to another cannot be exactly predicted. From the time the CLKPS values are written, it takes between T1 + T2 and T1 + 2*T2 before the new clock frequency is active. In this interval, 2 active clock edges are produced. Here, T1 is the previous clock period, and T2 is the period corresponding to the new prescaler setting. 7.12 7.12.1 Register Description OSCCAL - Oscillator Calibration Register Bit 0x31 (0x51) Read/Write 7 CAL7 R/W 6 CAL6 R/W 5 CAL5 R/W 4 CAL4 R/W 3 CAL3 R/W 2 CAL2 R/W 1 CAL1 R/W 0 CAL0 R/W OSCCAL Initial Value Device Specific Calibration Value * Bits 7:0 - CAL7:0: Oscillator Calibration Value The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to remove process variations from the oscillator frequency. A pre-programmed calibration value is automatically written to this register during chip reset, giving the Factory calibrated frequency as specified in Table 23-1 on page 189. The application software can write this register to change the oscillator frequency. The oscillator can be calibrated to frequencies as specified in Table 23-1 on page 189. Calibration outside that range is not guaranteed. Note that this oscillator is used to time EEPROM and Flash write accesses, and these write times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail. 32 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the lowest frequency range, setting this bit to 1 gives the highest frequency range. The two frequency ranges are overlapping, in other words a setting of OSCCAL = 0x7F gives a higher frequency than OSCCAL = 0x80. The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00 gives the lowest frequency in that range, and a setting of 0x7F gives the highest frequency in the range. 7.12.2 CLKPR - Clock Prescale Register Bit 0x28 (0x48) Read/Write Initial Value 7 CLKPCE R/W 0 6 - R 0 5 - R 0 4 - R 0 3 CLKPS3 R/W 2 CLKPS2 R/W 1 CLKPS1 R/W 0 CLKPS0 R/W CLKPR See Bit Description * Bit 7 - CLKPCE: Clock Prescaler Change Enable The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE bit is only updated when the other bits in CLKPR are simultaneously written to zero. CLKPCE is cleared by hardware four cycles after it is written or when the CLKPS bits are written. Rewriting the CLKPCE bit within this time-out period does neither extend the time-out period, nor clear the CLKPCE bit. * Bits 6:4 - Res: Reserved Bits These bits are reserved bits in the ATtiny261/461/861 and will always read as zero. * Bits 3:0 - CLKPS3:0: Clock Prescaler Select Bits 3 - 0 These bits define the division factor between the selected clock source and the internal system clock. These bits can be written run-time to vary the clock frequency to suit the application requirements. As the divider divides the master clock input to the MCU, the speed of all synchronous peripherals is reduced when a division factor is used. The division factors are given in Table 7-12. To avoid unintentional changes of clock frequency, a special write procedure must be followed to change the CLKPS bits: 1. Write the Clock Prescaler Change Enable (CLKPCE) bit to one and all other bits in CLKPR to zero. 2. Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE. Interrupts must be disabled when changing prescaler setting to make sure the write procedure is not interrupted. The CKDIV8 Fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed, the CLKPS bits will be reset to "0000". If CKDIV8 is programmed, CLKPS bits are reset to "0011", giving a division factor of eight at start up. This feature should be used if the selected clock source has a higher frequency than the maximum frequency of the device at the present operating conditions. Note that any value can be written to the CLKPS bits regardless of the CKDIV8 Fuse setting. The Application software must ensure that a sufficient division factor is chosen if the selected clock source has a higher frequency than the maximum frequency of the device at the present operating conditions. The device is shipped with the CKDIV8 Fuse programmed. 33 7753C-AVR-07/09 Table 7-12. CLKPS3 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 Clock Prescaler Select CLKPS2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 CLKPS1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 CLKPS0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Clock Division Factor 1 2 4 8 16 32 64 128 256 Reserved Reserved Reserved Reserved Reserved Reserved Reserved 34 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 8. Power Management and Sleep Modes The high performance and industry leading code efficiency makes the AVR microcontrollers an ideal choice for low power applications. Sleep modes enable the application to shut down unused modules in the MCU, thereby saving power. The AVR provides various sleep modes allowing the user to tailor the power consumption to the application's requirements. 8.1 Sleep Modes Figure 7-1 on page 25 presents the different clock systems in the ATtiny261/461/861, and their distribution. The figure is helpful in selecting an appropriate sleep mode. Table 8-1 shows the different sleep modes and their wake up sources. Table 8-1. Active Clock Domains and Wake-up Sources in the Different Sleep Modes Active Clock Domains Oscillators Main Clock Source Enabled INT0, INT1 and Pin Change Wake-up Sources SPM/EEPROM Ready Sleep Mode Idle ADC Noise Reduction Power-down Standby Note: X X X X X X X X(1) X(1) X (1) X X X X X X X X X X X X X 1. For INT0 and INT1, only level interrupt. To enter any of the three sleep modes, the SE bit in MCUCR must be written to logic one and a SLEEP instruction must be executed. The SM1..0 bits in the MCUCR Register select which sleep mode (Idle, ADC Noise Reduction, Power-down, or Standby) will be activated by the SLEEP instruction. See Table 8-2 for a summary. If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up. The MCU is then halted for four cycles in addition to the start-up time, executes the interrupt routine, and resumes execution from the instruction following SLEEP. The contents of the Register File and SRAM are unaltered when the device wakes up from sleep. If a reset occurs during sleep mode, the MCU wakes up and executes from the Reset Vector. 8.2 Idle Mode When the SM1..0 bits are written to 00, the SLEEP instruction makes the MCU enter Idle mode, stopping the CPU but allowing Analog Comparator, ADC, Timer/Counter, Watchdog, and the interrupt system to continue operating. This sleep mode basically halts clkCPU and clkFLASH, while allowing the other clocks to run. Idle mode enables the MCU to wake up from external triggered interrupts as well as internal ones like the Timer Overflow. If wake-up from the Analog Comparator interrupt is not required, the Analog Comparator can be powered down by setting the ACD bit in the Analog Comparator Control and Status Register - ACSR. This will reduce power consumption in Idle mode. If the ADC is enabled, a conversion starts automatically when this mode is entered. 35 7753C-AVR-07/09 Other I/O clkFLASH clkADC clkPCK clkCPU WDT ADC clkIO USI 8.3 ADC Noise Reduction Mode When the SM1..0 bits are written to 01, the SLEEP instruction makes the MCU enter ADC Noise Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, and the Watchdog to continue operating (if enabled). This sleep mode halts clkI/O, clkCPU, and clkFLASH, while allowing the other clocks to run. This improves the noise environment for the ADC, enabling higher resolution measurements. If the ADC is enabled, a conversion starts automatically when this mode is entered. Apart form the ADC Conversion Complete interrupt, only an External Reset, a Watchdog Reset, a Brown-out Reset, an SPM/EEPROM ready interrupt, an external level interrupt on INT0 or a pin change interrupt can wake up the MCU from ADC Noise Reduction mode. 8.4 Power-down Mode When the SM1..0 bits are written to 10, the SLEEP instruction makes the MCU enter Power-down mode. In this mode, the Oscillator is stopped, while the external interrupts, and the Watchdog continue operating (if enabled). Only an External Reset, a Watchdog Reset, a Brown-out Reset, an external level interrupt on INT0, or a pin change interrupt can wake up the MCU. This sleep mode halts all generated clocks, allowing operation of asynchronous modules only. Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed level must be held for some time to wake up the MCU. Refer to "External Interrupts" on page 52 for details. 8.5 Standby Mode When the SM1..0 bits are written to 11 and an external crystal/resonator clock option is selected, the SLEEP instruction makes the MCU enter Standby mode. This mode is identical to Power-down with the exception that the Oscillator is kept running. From Standby mode, the device wakes up in six clock cycles. 8.6 Power Reduction Register The Power Reduction Register (PRR), see "PRR - Power Reduction Register" on page 38, provides a method to stop the clock to individual peripherals to reduce power consumption. The current state of the peripheral is frozen and the I/O registers can not be read or written. Resources used by the peripheral when stopping the clock will remain occupied, hence the peripheral should in most cases be disabled before stopping the clock. Waking up a module, which is done by clearing the bit in PRR, puts the module in the same state as before shutdown. Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall power consumption. See "Supply Current of I/O modules" on page 199 for examples. In all other sleep modes, the clock is already stopped. 8.7 Minimizing Power Consumption There are several issues to consider when trying to minimize the power consumption in an AVR controlled system. In general, sleep modes should be used as much as possible, and the sleep mode should be selected so that as few as possible of the device's functions are operating. All functions not needed should be disabled. In particular, the following modules may need special consideration when trying to achieve the lowest possible power consumption. 36 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 8.7.1 Analog to Digital Converter If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be disabled before entering any sleep mode. When the ADC is turned off and on again, the next conversion will be an extended conversion. Refer to "ADC - Analog to Digital Converter" on page 144 for details on ADC operation. Analog Comparator When entering Idle mode, the Analog Comparator should be disabled if not used. When entering ADC Noise Reduction mode, the Analog Comparator should be disabled. In the other sleep modes, the Analog Comparator is automatically disabled. However, if the Analog Comparator is set up to use the Internal Voltage Reference as input, the Analog Comparator should be disabled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled, independent of sleep mode. Refer to "AC - Analog Comparator" on page 140 for details on how to configure the Analog Comparator. Brown-out Detector If the Brown-out Detector is not needed in the application, this module should be turned off. If the Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in all sleep modes, and hence, always consume power. In the deeper sleep modes, this will contribute significantly to the total current consumption. Refer to "Brown-out Detection" on page 43 for details on how to configure the Brown-out Detector. Internal Voltage Reference The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, the Analog Comparator or the ADC. If these modules are disabled as described in the sections above, the internal voltage reference will be disabled and it will not be consuming power. When turned on again, the user must allow the reference to start up before the output is used. If the reference is kept on in sleep mode, the output can be used immediately. Refer to "Internal Voltage Reference" on page 44 for details on the start-up time. Watchdog Timer If the Watchdog Timer is not needed in the application, this module should be turned off. If the Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence, always consume power. In the deeper sleep modes, this will contribute significantly to the total current consumption. Refer to "Watchdog Timer" on page 44 for details on how to configure the Watchdog Timer. Port Pins When entering a sleep mode, all port pins should be configured to use minimum power. The most important thing is then to ensure that no pins drive resistive loads. In sleep modes where both the I/O clock (clkI/O) and the ADC clock (clkADC) are stopped, the input buffers of the device will be disabled. This ensures that no power is consumed by the input logic when not needed. In some cases, the input logic is needed for detecting wake-up conditions, and it will then be enabled. Refer to the section "Digital Input Enable and Sleep Modes" on page 59 for details on which pins are enabled. If the input buffer is enabled and the input signal is left floating or has an analog signal level close to VCC/2, the input buffer will use excessive power. 8.7.2 8.7.3 8.7.4 8.7.5 8.7.6 37 7753C-AVR-07/09 For analog input pins, the digital input buffer should be disabled at all times. An analog signal level close to VCC/2 on an input pin can cause significant current even in active mode. Digital input buffers can be disabled by writing to the Digital Input Disable Registers (DIDR0, DIDR1). Refer to "DIDR0 - Digital Input Disable Register 0" on page 163 or "DIDR1 - Digital Input Disable Register 1" on page 163 for details. 8.8 8.8.1 Register Description MCUCR - MCU Control Register The MCU Control Register contains control bits for power management. Bit 0x35 (0x55) Read/Write Initial Value 7 - R 0 6 PUD R/W 0 5 SE R/W 0 4 SM1 R/W 0 3 SM0 R/W 0 2 -- R 0 1 ISC01 R/W 0 0 ISC00 R/W 0 MCUCR * Bit 5 - SE: Sleep Enable The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP instruction is executed. To avoid the MCU entering the sleep mode unless it is the programmer's purpose, it is recommended to write the Sleep Enable (SE) bit to one just before the execution of the SLEEP instruction and to clear it immediately after waking up. * Bits 4, 3 - SM1:0: Sleep Mode Select Bits 2..0 These bits select between the three available sleep modes as shown in Table 8-2. Table 8-2. SM1 0 0 1 1 Sleep Mode Select SM0 0 1 0 1 Sleep Mode Idle ADC Noise Reduction Power-down Standby * Bit 2 - Res: Reserved Bit This bit is a reserved ed bit in the ATtiny261/461/861 and will always read as zero. 8.8.2 PRR - Power Reduction Register Bit 0x36 (0x56) Read/Write Initial Value 7 - R 0 6 R 0 5 R 0 4 R 0 3 PRTIM1 R/W 0 2 PRTIM0 R/W 0 1 PRUSI R/W 0 0 PRADC R/W 0 PRR * Bits 7, 6, 5, 4- Res: Reserved Bits These bits are reserved bits in the ATtiny261/461/861 and will always read as zero. 38 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 * Bit 3- PRTIM1: Power Reduction Timer/Counter1 Writing a logic one to this bit shuts down the Timer/Counter1 module. When the Timer/Counter1 is enabled, operation will continue like before the shutdown. * Bit 2- PRTIM0: Power Reduction Timer/Counter0 Writing a logic one to this bit shuts down the Timer/Counter0 module. When the Timer/Counter0 is enabled, operation will continue like before the shutdown. * Bit 1 - PRUSI: Power Reduction USI Writing a logic one to this bit shuts down the USI by stopping the clock to the module. When waking up the USI again, the USI should be re initialized to ensure proper operation. * Bit 0 - PRADC: Power Reduction ADC Writing a logic one to this bit shuts down the ADC. The ADC must be disabled before shut down. Also analog comparator needs this clock. 39 7753C-AVR-07/09 9. System Control and Reset 9.0.1 Resetting the AVR During reset, all I/O Registers are set to their initial values, and the program starts execution from the Reset Vector. The instruction placed at the Reset Vector must be a RJMP - Relative Jump - instruction to the reset handling routine. If the program never enables an interrupt source, the Interrupt Vectors are not used, and regular program code can be placed at these locations. The circuit diagram in Figure 9-1 shows the reset logic. "System and Reset Characteristics" on page 190 defines the electrical parameters of the reset circuitry. The I/O ports of the AVR are immediately reset to their initial state when a reset source goes active. This does not require any clock source to be running. After all reset sources have gone inactive, a delay counter is invoked, stretching the internal reset. This allows the power to reach a stable level before normal operation starts. The time-out period of the delay counter is defined by the user through the SUT and CKSEL Fuses. The different selections for the delay period are presented in "Clock Sources" on page 27. 9.0.2 Reset Sources The ATtiny261/461/861 has four sources of reset: * Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset threshold (VPOT). * External Reset. The MCU is reset when a low level is present on the RESET pin for longer than the minimum pulse length. * Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and the Watchdog is enabled. * Brown-out Reset. The MCU is reset when the supply voltage VCC is below the Brown-out Reset threshold (VBOT) and the Brown-out Detector is enabled. 40 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 9-1. Reset Logic DATA BUS MCU Status Register (MCUSR) PORF BORF EXTRF WDRF Power-on Reset Circuit BODLEVEL [1..0] Pull-up Resistor SPIKE FILTER Brown-out Reset Circuit Watchdog Oscillator Clock Generator CK Delay Counters TIMEOUT CKSEL[1:0] SUT[1:0] 9.0.3 Power-on Reset A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level is defined in "System and Reset Characteristics" on page 190. The POR is activated whenever VCC is below the detection level. The POR circuit can be used to trigger the Start-up Reset, as well as to detect a failure in supply voltage. A Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reaching the Power-on Reset threshold voltage invokes the delay counter, which determines how long the device is kept in RESET after VCC rise. The RESET signal is activated again, without any delay, when VCC decreases below the detection level. Figure 9-2. VCC VPORMAX VPORMIN RESET V RST TIME-OUT t TOUT MCU Start-up, RESET Tied to VCC VCCRR INTERNAL RESET 41 7753C-AVR-07/09 Figure 9-3. VCC MCU Start-up, RESET Extended Externally VPOT RESET V RST TIME-OUT INTERNAL RESET t TOUT Table 9-1. Symbol VPOT VPORMAX VPORMIN VCCRR VRST Note: Power On Reset Specifications Parameter Power-on Reset Threshold Voltage (rising) Power-on Reset Threshold Voltage (falling) VCC Max. start voltage to ensure internal Power-on Reset signal VCC Min. start voltage to ensure internal Power-on Reset signal VCC Rise Rate to ensure Power-on Reset RESET Pin Threshold Voltage -0.1 0.01 0.1 VCC 0.9VCC (1) Min 1.1 0.8 Typ 1.4 1.3 Max 1.7 1.6 0.4 Unit V V V V V/ms V 1. Before rising, the supply has to be between VPORMIN and VPORMAX to ensure a Reset. 9.0.4 External Reset An External Reset is generated by a low level on the RESET pin if enabled. Reset pulses longer than the minimum pulse width (see "System and Reset Characteristics" on page 190) will generate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate a reset. When the applied signal reaches the Reset Threshold Voltage - VRST - on its positive edge, the delay counter starts the MCU after the Time-out period - tTOUT - has expired. Figure 9-4. CC External Reset During Operation 42 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 9.0.5 Brown-out Detection ATtiny261/461/861 has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC level during operation by comparing it to a fixed trigger level. The trigger level for the BOD can be selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike free Brown-out Detection. The hysteresis on the detection level should be interpreted as VBOT+ = VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2. When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure 9-5), the Brown-out Reset is immediately activated. When VCC increases above the trigger level (VBOT+ in Figure 9-5), the delay counter starts the MCU after the Time-out period tTOUT has expired. The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for longer than tBOD given in "System and Reset Characteristics" on page 190. Figure 9-5. Brown-out Reset During Operation VCC VBOTVBOT+ RESET TIME-OUT tTOUT INTERNAL RESET 9.0.6 Watchdog Reset When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On the falling edge of this pulse, the delay timer starts counting the Time-out period tTOUT. Refer to page 44 for details on operation of the Watchdog Timer. Figure 9-6. CC Watchdog Reset During Operation CK 43 7753C-AVR-07/09 9.1 Internal Voltage Reference ATtiny261/461/861 features an internal bandgap reference. This reference is used for Brown-out Detection, and it can be used as an input to the Analog Comparator or the ADC. 9.1.1 Voltage Reference Enable Signals and Start-up Time The voltage reference has a start-up time that may influence the way it should be used. The start-up time is given in "System and Reset Characteristics" on page 190. To save power, the reference is not always turned on. The reference is on during the following situations: 1. When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse bits). 2. When the bandgap reference is connected to the Analog Comparator (by setting the ACBG bit in ACSR). 3. When the ADC is enabled. Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user must always allow the reference to start up before the output from the Analog Comparator or ADC is used. To reduce power consumption in Power-down mode, the user can avoid the three conditions above to ensure that the reference is turned off before entering Power-down mode. 9.2 Watchdog Timer The Watchdog Timer is clocked from an On-chip Oscillator which runs at 128 kHz. By controlling the Watchdog Timer prescaler, the Watchdog Reset interval can be adjusted as shown in Table 9-4 on page 48. The WDR - Watchdog Reset - instruction resets the Watchdog Timer. The Watchdog Timer is also reset when it is disabled and when a Chip Reset occurs. Ten different clock cycle periods can be selected to determine the reset period. If the reset period expires without another Watchdog Reset, the ATtiny261/461/861 resets and executes from the Reset Vector. For timing details on the Watchdog Reset, refer to Table 9-4 on page 48. The Watchdog Timer can also be configured to generate an interrupt instead of a reset. This can be very helpful when using the Watchdog to wake-up from Power-down. To prevent unintentional disabling of the Watchdog or unintentional change of time-out period, two different safety levels are selected by the fuse WDTON as shown in Table 9-2. Refer to "Timed Sequences for Changing the Configuration of the Watchdog Timer" on page 45 for details. Table 9-2. WDTON WDT Configuration as a Function of the Fuse Settings of WDTON Safety Level 1 2 WDT Initial State Disabled Enabled How to Disable the WDT Timed sequence Always enabled How to Change Time-out No limitations Timed sequence Unprogrammed Programmed 44 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 9-7. Watchdog Timer 128 kHz OSCILLATOR OSC/2K OSC/4K OSC/8K WATCHDOG PRESCALER OSC/1024K OSC/128K OSC/256K OSC/512K OSC/16K OSC/32K OSC/64K WATCHDOG RESET WDP0 WDP1 WDP2 WDP3 WDE MCU RESET 9.3 Timed Sequences for Changing the Configuration of the Watchdog Timer The sequence for changing configuration differs slightly between the two safety levels. Separate procedures are described for each level. 9.3.1 Safety Level 1 In this mode, the Watchdog Timer is initially disabled, but can be enabled by writing the WDE bit to one without any restriction. A timed sequence is needed when disabling an enabled Watchdog Timer. To disable an enabled Watchdog Timer, the following procedure must be followed: 1. In the same operation, write a logic one to WDCE and WDE. A logic one must be written to WDE regardless of the previous value of the WDE bit. 2. Within the next four clock cycles, in the same operation, write the WDE and WDP bits as desired, but with the WDCE bit cleared. 9.3.2 Safety Level 2 In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read as one. A timed sequence is needed when changing the Watchdog Time-out period. To change the Watchdog Time-out, the following procedure must be followed: 1. In the same operation, write a logical one to WDCE and WDE. Even though the WDE always is set, the WDE must be written to one to start the timed sequence. 2. Within the next four clock cycles, in the same operation, write the WDP bits as desired, but with the WDCE bit cleared. The value written to the WDE bit is irrelevant. 9.4 9.4.1 Register Description MCUSR - MCU Status Register The MCU Status Register provides information on which reset source caused an MCU Reset. Bit 0x34 (0x54) Read/Write Initial Value 7 - R 0 6 - R 0 5 - R 0 4 - R 0 3 WDRF R/W 2 BORF R/W 1 EXTRF R/W 0 PORF R/W MCUSR See Bit Description 45 7753C-AVR-07/09 * Bits 7:4 - Res: Reserved Bits These bits are reserved bits in the ATtiny261/461/861 and will always read as zero. * Bit 3 - WDRF: Watchdog Reset Flag This bit is set if a Watchdog Reset occurs. The bit is reset by a Power-on Reset, or by writing a logic zero to the flag. * Bit 2 - BORF: Brown-out Reset Flag This bit is set if a Brown-out Reset occurs. The bit is reset by a Power-on Reset, or by writing a logic zero to the flag. * Bit 1 - EXTRF: External Reset Flag This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by writing a logic zero to the flag. * Bit 0 - PORF: Power-on Reset Flag This bit is set if a Power-on Reset occurs. The bit is reset only by writing a logic zero to the flag. To make use of the Reset Flags to identify a reset condition, the user should read and then reset the MCUSR as early as possible in the program. If the register is cleared before another reset occurs, the source of the reset can be found by examining the Reset Flags. 9.4.2 WDTCR - Watchdog Timer Control Register Bit 0x21 (0x41) Read/Write Initial Value 7 WDIF R/W 0 6 WDIE R/W 0 5 WDP3 R/W 0 4 WDCE R/W 0 3 WDE R/W X 2 WDP2 R/W 0 1 WDP1 R/W 0 0 WDP0 R/W 0 WDTCR * Bit 7 - WDIF: Watchdog Timeout Interrupt Flag This bit is set when a time-out occurs in the Watchdog Timer and the Watchdog Timer is configured for interrupt. WDIF is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, WDIF is cleared by writing a logic one to the flag. When the I-bit in SREG and WDIE are set, the Watchdog Time-out Interrupt is executed. * Bit 6 - WDIE: Watchdog Timeout Interrupt Enable When this bit is written to one, WDE is cleared, and the I-bit in the Status Register is set, the Watchdog Time-out Interrupt is enabled. In this mode the corresponding interrupt is executed instead of a reset if a timeout in the Watchdog Timer occurs. If WDE is set, WDIE is automatically cleared by hardware when a time-out occurs. This is useful for keeping the Watchdog Reset security while using the interrupt. After the WDIE bit is cleared, the next time-out will generate a reset. To avoid the Watchdog Reset, WDIE must be set after each interrupt. 46 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 9-3. WDE 0 0 1 1 Watchdog Timer Configuration WDIE 0 1 0 1 Watchdog Timer State Stopped Running Running Running Action on Time-out None Interrupt Reset Interrupt * Bit 4 - WDCE: Watchdog Change Enable This bit must be set when the WDE bit is written to logic zero. Otherwise, the Watchdog will not be disabled. Once written to one, hardware will clear this bit after four clock cycles. Refer to the description of the WDE bit for a Watchdog disable procedure. This bit must also be set when changing the prescaler bits. See "Timed Sequences for Changing the Configuration of the Watchdog Timer" on page 45. * Bit 3 - WDE: Watchdog Enable When the WDE is written to logic one, the Watchdog Timer is enabled, and if the WDE is written to logic zero, the Watchdog Timer function is disabled. WDE can only be cleared if the WDCE bit has logic level one. To disable an enabled Watchdog Timer, the following procedure must be followed: 1. In the same operation, write a logic one to WDCE and WDE. A logic one must be written to WDE even though it is set to one before the disable operation starts. 2. Within the next four clock cycles, write a logic 0 to WDE. This disables the Watchdog. In safety level 2, it is not possible to disable the Watchdog Timer, even with the algorithm described above. See "Timed Sequences for Changing the Configuration of the Watchdog Timer" on page 45. In safety level 1, WDE is overridden by WDRF in MCUSR. See "MCUSR - MCU Status Register" on page 45 for description of WDRF. This means that WDE is always set when WDRF is set. To clear WDE, WDRF must be cleared before disabling the Watchdog with the procedure described above. This feature ensures multiple resets during conditions causing failure, and a safe start-up after the failure. Note: If the watchdog timer is not going to be used in the application, it is important to go through a watchdog disable procedure in the initialization of the device. If the Watchdog is accidentally enabled, for example by a runaway pointer or brown-out condition, the device will be reset, which in turn will lead to a new watchdog reset. To avoid this situation, the application software should always clear the WDRF flag and the WDE control bit in the initialization routine. * Bits 5, 2:0 - WDP3..0: Watchdog Timer Prescaler 3, 2, 1, and 0 The WDP3..0 bits determine the Watchdog Timer prescaling when the Watchdog Timer is enabled. The different prescaling values and their corresponding Timeout Periods are shown in Table 9-4 on page 48. 47 7753C-AVR-07/09 Table 9-4. WDP3 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 Notes: Watchdog Timer Prescale Select WDP2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 WDP1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 WDP0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Reserved(1) Number of WDT Oscillator Cycles 2K (2048) cycles 4K (4096) cycles 8K (8192) cycles 16K (16384) cycles 32K (32764) cycles 64K (65536) cycles 128K (131072) cycles 256K (262144) cycles 512K (524288) cycles 1024K (1048576) cycles Typical Time-out at VCC = 5.0V 16 ms 32 ms 64 ms 0.125 s 0.25 s 0.5 s 1.0 s 2.0 s 4.0 s 8.0 s 1. If selecting a reserved code WDT time-out is selected to be one of the legal selections. 48 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 The following code example shows one assembly and one C function for turning off the WDT. The example assumes that interrupts are controlled (e.g., by disabling interrupts globally) so that no interrupts will occur during execution of these functions. Assembly Code Example(1) WDT_off: WDR ; Clear WDRF in MCUSR ldi out r16, (0< void WDT_off(void) { _WDR(); /* Clear WDRF in MCUSR */ MCUSR = 0x00 /* Write logical one to WDCE and WDE */ WDTCR |= (1< 7753C-AVR-07/09 10. Interrupts This section describes the specifics of the interrupt handling as performed in ATtiny261/461/861. For a general explanation of the AVR interrupt handling, refer to "Reset and Interrupt Handling" on page 15. 10.1 Interrupt Vectors in ATtiny261/461/861 Table 10-1. Vector No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Reset and Interrupt Vectors Program Address 0x0000 0x0001 0x0002 0x0003 0x0004 0x0005 0x0006 0x0007 0x0008 0x0009 0x000A 0x000B 0x000C 0x000D 0x000E 0x000F 0x0010 0x0011 0x0012 Source RESET INT0 PCINT TIMER1_COMPA TIMER1_COMPB TIMER1_OVF TIMER0_OVF USI_START USI_OVF EE_RDY ANA_COMP ADC WDT INT1 TIMER0_COMPA TIMER0_COMPB TIMER0_CAPT TIMER1_COMPD FAULT_PROTECTION Interrupt Definition External Pin, Power-on Reset, Brown-out Reset, Watchdog Reset External Interrupt Request 0 Pin Change Interrupt Request Timer/Counter1 Compare Match A Timer/Counter1 Compare Match B Timer/Counter1 Overflow Timer/Counter0 Overflow USI Start USI Overflow EEPROM Ready Analog Comparator ADC Conversion Complete Watchdog Time-out External Interrupt Request 1 Timer/Counter0 Compare Match A Timer/Counter0 Compare Match B Timer/Counter1 Capture Event Timer/Counter1 Compare Match D Timer/Counter1 Fault Protection If the program never enables an interrupt source, the Interrupt Vectors are not used, and regular program code can be placed at these locations. The most typical and general program setup for the Reset and Interrupt Vector Addresses in ATtiny261/461/861 is: 50 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Address Labels Code 0x0000 0x0001 0x0002 0x0003 0x0004 0x0005 0x0006 0x0007 0x0008 0x0009 0x000A 0x000B 0x000C 0x000D 0x000E 0x000F 0x0010 0x0011 0x0012 0x0013 0x0014 0x0015 0x0016 0x0017 0x0018 ... ... rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp rjmp RESET: ldi ldi out out sei FAULT_PROTECTION ; Timer1 Fault Protection r16, low(RAMEND) ; Main program start r17, high(RAMEND); Tiny861 have also SPH SPL, r16 SPH, r17 ; Set Stack Pointer to top of RAM ; Tiny861 have also SPH ; Enable interrupts 51 7753C-AVR-07/09 11. External Interrupts The External Interrupts are triggered by the INT0 or INT1 pin or any of the PCINT15..0 pins. Observe that, if enabled, the interrupts will trigger even if the INT0, INT1 or PCINT15..0 pins are configured as outputs. This feature provides a way of generating a software interrupt. Pin change interrupts PCI will trigger if any enabled PCINT15..0 pin toggles. The PCMSK Register control which pins contribute to the pin change interrupts. Pin change interrupts on PCINT15..0 are detected asynchronously. This implies that these interrupts can be used for waking the part also from sleep modes other than Idle mode. The INT0 and INT1 interrupts can be triggered by a falling or rising edge or a low level. This is set up as indicated in the specification for the MCU Control Register - MCUCR. When the INT0 interrupt is enabled and is configured as level triggered, the interrupt will trigger as long as the pin is held low. Note that recognition of falling or rising edge interrupts on INT0 or INT1 requires the presence of an I/O clock, described in "Clock Systems and their Distribution" on page 25. Low level interrupt on INT0 is detected asynchronously. This implies that this interrupt can be used for waking the part also from sleep modes other than Idle mode. The I/O clock is halted in all sleep modes except Idle mode. Note that if a level triggered interrupt is used for wake-up from Power-down, the required level must be held long enough for the MCU to complete the wake-up to trigger the level interrupt. If the level disappears before the end of the Start-up Time, the MCU will still wake up, but no interrupt will be generated. The start-up time is defined by the SUT and CKSEL Fuses as described in "System Clock and Clock Options" on page 25. 11.1 11.1.1 Register Description MCUCR - MCU Control Register The MCU Register contains control bits for interrupt sense control. Bit 0x35 (0x55) Read/Write Initial Value 7 - R 0 6 PUD R/W 0 5 SE R/W 0 4 SM1 R/W 0 3 SM0 R/W 0 2 - R 0 1 ISC01 R/W 0 0 ISC00 R/W 0 MCUCR * Bits 1, 0 - ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0 The External Interrupt 0 is activated by the external pin INT0 or INT1 if the SREG I-flag and the corresponding interrupt mask are set. The level and edges on the external INT0 or INT1 pin that activate the interrupt are defined in Table 11-1. The value on the INT0 or INT1 pin is sampled before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one clock period will generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low level interrupt is selected, the low level must be held until the completion of the currently executing instruction to generate an interrupt. Table 11-1. ISC01 0 0 1 1 Interrupt 0 Sense Control ISC00 0 1 0 1 Description The low level of INT0 or INT1 generates an interrupt request. Any logical change on INT0 or INT1 generates an interrupt request. The falling edge of INT0 or INT1 generates an interrupt request. The rising edge of INT0 or INT1 generates an interrupt request. 52 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 11.1.2 GIMSK - General Interrupt Mask Register Bit 0x3B (0x5B) Read/Write Initial Value 7 INT1 R/W 0 6 INT0 R/W 0 5 PCIE1 R/W 0 4 PCIE0 R/w 0 3 - R 0 2 - R 0 1 - R 0 0 - R 0 GIMSK * Bit 7 - INT1: External Interrupt Request 1 Enable When the INT1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the external pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and ISC00) in the MCU Control Register (MCUCR) define whether the external interrupt is activated on rising and/or falling edge of the INT1 pin or level sensed. Activity on the pin will cause an interrupt request even if INT1 is configured as an output. The corresponding interrupt of External Interrupt Request 1 is executed from the INT1 Interrupt Vector. * Bit 6 - INT0: External Interrupt Request 0 Enable When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the external pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and ISC00) in the MCU Control Register (MCUCR) define whether the external interrupt is activated on rising and/or falling edge of the INT0 pin or level sensed. Activity on the pin will cause an interrupt request even if INT0 is configured as an output. The corresponding interrupt of External Interrupt Request 0 is executed from the INT0 Interrupt Vector. * Bit 5 - PCIE1: Pin Change Interrupt Enable When the PCIE1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin change interrupt is enabled. Any change on any enabled PCINT7..0 or PCINT15..12 pin will cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI Interrupt Vector. PCINT7..0 and PCINT15..12 pins are enabled individually by the PCMSK0 and PCMSK1 Register. * Bit 4 - PCIE0: Pin Change Interrupt Enable When the PCIE0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin change interrupt is enabled. Any change on any enabled PCINT11..8 pin will cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI Interrupt Vector. PCINT11..8 pins are enabled individually by the PCMSK1 Register. * Bits 3..0 - Res: Reserved Bits These bits are reserved bits in the ATtiny261/461/861 and will always read as zero. 11.1.3 GIFR - General Interrupt Flag Register Bit 0x3A (0x5A) Read/Write Initial Value 7 INT1 R/W 0 6 INTF0 R/W 0 5 PCIF R/W 0 4 - R 0 3 - R 0 2 - R 0 1 - R 0 0 - R 0 GIFR * Bit 7- INTF1: External Interrupt Flag 1 When an edge or logic change on the INT1 pin triggers an interrupt request, INTF1 becomes set (one). If the I-bit in SREG and the INT1 bit in GIMSK are set (one), the MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. 53 7753C-AVR-07/09 Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared when INT1 is configured as a level interrupt. * Bit 6 - INTF0: External Interrupt Flag 0 When an edge or logic change on the INT0 pin triggers an interrupt request, INTF0 becomes set (one). If the I-bit in SREG and the INT0 bit in GIMSK are set (one), the MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared when INT0 is configured as a level interrupt. * Bit 5 - PCIF: Pin Change Interrupt Flag When a logic change on any PCINT15 pin triggers an interrupt request, PCIF becomes set (one). If the I-bit in SREG and the PCIE bit in GIMSK are set (one), the MCU will jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it. * Bits 4:0 - Res: Reserved Bits These bits are reserved bits in the ATtiny261/461/861 and will always read as zero. 11.1.4 PCMSK0 - Pin Change Mask Register A Bit 0x23 (0x43) Read/Write Initial Value 7 PCINT7 R/W 1 6 PCINT6 R/W 1 5 PCINT5 R/W 0 4 PCINT4 R/w 0 3 PCINT3 R/W 1 2 PCINT2 R/W 0 1 PCINT1 R/W 0 0 PCINT0 R/W 0 PCMSK0 * Bits 7:0 - PCINT7:0: Pin Change Enable Mask 7..0 Each PCINT7:0 bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT7:0 is set and the PCIE1 bit in GIMSK is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT7..0 is cleared, pin change interrupt on the corresponding I/O pin is disabled. 11.1.5 PCMSK1 - Pin Change Mask Register B Bit 0x22 (0x42) Read/Write Initial Value 7 PCINT15 R/W 1 6 PCINT14 R/W 1 5 PCINT13 R/W 1 4 PCINT12 R/w 1 3 PCINT11 R/W 1 2 PCINT10 R/W 1 1 PCINT9 R/W 1 0 PCINT8 R/W 1 PCMSK1 * Bits 7:0 - PCINT15:8: Pin Change Enable Mask 15..8 Each PCINT15:8 bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT11:8 is set and the PCIE0 bit in GIMSK is set, pin change interrupt is enabled on the corresponding I/O pin, and if PCINT15:12 is set and the PCIE1 bit in GIMSK is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT15:8 is cleared, pin change interrupt on the corresponding I/O pin is disabled. 54 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 12. I/O Ports 12.1 Overview All AVR ports have true Read-Modify-Write functionality when used as general digital I/O ports. This means that the direction of one port pin can be changed without unintentionally changing the direction of any other pin with the SBI and CBI instructions. The same applies when changing drive value (if configured as output) or enabling/disabling of pull-up resistors (if configured as input). Each output buffer has symmetrical drive characteristics with both high sink and source capability. The pin driver is strong enough to drive LED displays directly. All port pins have individually selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins have protection diodes to both VCC and Ground as indicated in Figure 12-1. Refer to "Electrical Characteristics" on page 187 for a complete list of parameters. Figure 12-1. I/O Pin Equivalent Schematic RPU Pxn Logic CPIN See Figure "General Digital I/O" for Details All registers and bit references in this section are written in general form. A lower case "x" represents the numbering letter for the port, and a lower case "n" represents the bit number. However, when using the register or bit defines in a program, the precise form must be used. For example, PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The physical I/O Registers and bit locations are listed in "Register Description" on page 69. Three I/O memory address locations are allocated for each port, one each for the Data Register - PORTx, Data Direction Register - DDRx, and the Port Input Pins - PINx. The Port Input Pins I/O location is read only, while the Data Register and the Data Direction Register are read/write. However, writing a logic one to a bit in the PINx Register, will result in a toggle in the corresponding bit in the Data Register. In addition, the Pull-up Disable - PUD bit in MCUCR disables the pull-up function for all pins in all ports when set. Using the I/O port as General Digital I/O is described in "Ports as General Digital I/O" on page 56. Most port pins are multiplexed with alternate functions for the peripheral features on the device. How each alternate function interferes with the port pin is described in "Alternate Port Functions" on page 60. Refer to the individual module sections for a full description of the alternate functions. 55 7753C-AVR-07/09 Note that enabling the alternate function of some of the port pins does not affect the use of the other pins in the port as general digital I/O. 12.2 Ports as General Digital I/O The ports are bi-directional I/O ports with optional internal pull-ups. Figure 12-2 shows a functional description of one I/O-port pin, here generically called Pxn. Figure 12-2. General Digital I/O(1) PUD Q D DDxn Q CLR RESET WDx RDx 1 Pxn Q D PORTxn Q CLR 0 RESET WRx SLEEP RRx WPx SYNCHRONIZER D Q D Q RPx PINxn L Q Q clk I/O PUD: SLEEP: clkI/O: PULLUP DISABLE SLEEP CONTROL I/O CLOCK WDx: RDx: WRx: RRx: RPx: WPx: WRITE DDRx READ DDRx WRITE PORTx READ PORTx REGISTER READ PORTx PIN WRITE PINx REGISTER Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, SLEEP, and PUD are common to all ports. 12.2.1 Configuring the Pin Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in "Register Description" on page 69, the DDxn bits are accessed at the DDRx I/O address, the PORTxn bits at the PORTx I/O address, and the PINxn bits at the PINx I/O address. The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written logic one, Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input pin. If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is activated. To switch the pull-up resistor off, PORTxn has to be written logic zero or the pin has to be configured as an output pin. The port pins are tri-stated when reset condition becomes active, even if no clocks are running. 56 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 DATA BUS ATtiny261/ATtiny461/ATtiny861 If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port pin is driven low (zero). 12.2.2 Toggling the Pin Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn. Note that the SBI instruction can be used to toggle one single bit in a port. Switching Between Input and Output When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn, PORTxn} = 0b11), an intermediate state with either pull-up enabled {DDxn, PORTxn} = 0b01) or output low ({DDxn, PORTxn} = 0b10) must occur. Normally, the pull-up enabled state is fully acceptable, as a high-impedent environment will not notice the difference between a strong high driver and a pull-up. If this is not the case, the PUD bit in the MCUCR Register can be set to disable all pull-ups in all ports. Switching between input with pull-up and output low generates the same problem. The user must use either the tri-state ({DDxn, PORTxn} = 0b00) or the output high state ({DDxn, PORTxn} = 0b10) as an intermediate step. Table 12-1 summarizes the control signals for the pin value. Table 12-1. DDxn 0 0 0 1 1 12.2.3 Port Pin Configurations PUD (in MCUCR) X 0 1 X X I/O Input Input Input Output Output Pull-up No Yes No No No Comment Tri-state (Hi-Z) Pxn will source current if ext. pulled low. Tri-state (Hi-Z) Output Low (Sink) Output High (Source) PORTxn 0 1 1 0 1 12.2.4 Reading the Pin Value Independent of the setting of Data Direction bit DDxn, the port pin can be read through the PINxn Register bit. As shown in Figure 12-2, the PINxn Register bit and the preceding latch constitute a synchronizer. This is needed to avoid metastability if the physical pin changes value near the edge of the internal clock, but it also introduces a delay. Figure 12-3 shows a timing diagram of the synchronization when reading an externally applied pin value. The maximum and minimum propagation delays are denoted tpd,max and tpd,min respectively. 57 7753C-AVR-07/09 Figure 12-3. Synchronization when Reading an Externally Applied Pin value SYSTEM CLK INSTRUCTIONS SYNC LATCH PINxn r17 0x00 t pd, max t pd, min 0xFF XXX XXX in r17, PINx Consider the clock period starting shortly after the first falling edge of the system clock. The latch is closed when the clock is low, and goes transparent when the clock is high, as indicated by the shaded region of the "SYNC LATCH" signal. The signal value is latched when the system clock goes low. It is clocked into the PINxn Register at the succeeding positive clock edge. As indicated by the two arrows tpd, max and tpd, min, a single signal transition on the pin will be delayed between 1/2 and 11/2 system clock period depending upon the time of assertion. When reading back a software assigned pin value, a nop instruction must be inserted as indicated in Figure 12-4. The out instruction sets the "SYNC LATCH" signal at the positive edge of the clock. In this case, the delay tpd through the synchronizer is one system clock period. Figure 12-4. Synchronization when Reading a Software Assigned Pin Value SYSTEM CLK r16 INSTRUCTIONS SYNC LATCH PINxn r17 0x00 t pd 0xFF out PORTx, r16 nop 0xFF in r17, PINx The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define the port pins from 4 to 5 as input with a pull-up assigned to port pin 4. The resulting pin values are read back again, but as previously discussed, a nop instruction is included to be able to read back the value recently assigned to some of the pins. 58 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Assembly Code Example(1) ... ; Define pull-ups and set outputs high ; Define directions for port pins ldi ldi out out nop ; Read port pins in ... r16,PINB r16,(1< C Code Example unsigned char i; ... /* Define pull-ups and set outputs high */ /* Define directions for port pins */ PORTB = (1< Digital Input Enable and Sleep Modes As shown in Figure 12-2, the digital input signal can be clamped to ground at the input of the schmitt-trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in Power-down mode, Power-save mode, and Standby mode to avoid high power consumption if some input signals are left floating, or have an analog signal level close to VCC/2. SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt request is not enabled, SLEEP is active also for these pins. SLEEP is also overridden by various other alternate functions as described in "Alternate Port Functions" on page 60. If a logic high level ("one") is present on an asynchronous external interrupt pin configured as "Interrupt on Rising Edge, Falling Edge, or Any Logic Change on Pin" while the external interrupt is not enabled, the corresponding External Interrupt Flag will be set when resuming from the above mentioned Sleep mode, as the clamping in these sleep mode produces the requested logic change. 59 7753C-AVR-07/09 12.2.6 Unconnected Pins If some pins are unused, it is recommended to ensure that these pins have a defined level. Even though most of the digital inputs are disabled in the deep sleep modes as described above, floating inputs should be avoided to reduce current consumption in all other modes where the digital inputs are enabled (Reset, Active mode and Idle mode). The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up. In this case, the pull-up will be disabled during reset. If low power consumption during reset is important, it is recommended to use an external pull-up or pull-down. Connecting unused pins directly to VCC or GND is not recommended, since this may cause excessive currents if the pin is accidentally configured as an output. 12.3 Alternate Port Functions Most port pins have alternate functions in addition to being general digital I/Os. Figure 12-5 shows how the port pin control signals from the simplified Figure 12-2 can be overridden by alternate functions. The overriding signals may not be present in all port pins, but the figure serves as a generic description applicable to all port pins in the AVR microcontroller family. 60 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 12-5. Alternate Port Functions(1) PUOExn PUOVxn 1 0 PUD DDOExn DDOVxn 1 0 QD DDxn Q CLR PVOExn PVOVxn WDx RESET RDx 1 Pxn 0 Q D 1 0 PORTxn PTOExn WPx DIEOExn DIEOVxn 1 0 Q CLR RESET RRx WRx SLEEP SYNCHRONIZER D SET RPx Q D Q PINxn L CLR Q CLR Q clk I/O DIxn AIOxn PUOExn: PUOVxn: DDOExn: DDOVxn: PVOExn: PVOVxn: DIEOExn: DIEOVxn: SLEEP: PTOExn: Pxn PULL-UP OVERRIDE ENABLE Pxn PULL-UP OVERRIDE VALUE Pxn DATA DIRECTION OVERRIDE ENABLE Pxn DATA DIRECTION OVERRIDE VALUE Pxn PORT VALUE OVERRIDE ENABLE Pxn PORT VALUE OVERRIDE VALUE Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE SLEEP CONTROL Pxn, PORT TOGGLE OVERRIDE ENABLE PUD: WDx: RDx: RRx: WRx: RPx: WPx: clkI/O: DIxn: AIOxn: PULLUP DISABLE WRITE DDRx READ DDRx READ PORTx REGISTER WRITE PORTx READ PORTx PIN WRITE PINx I/O CLOCK DIGITAL INPUT PIN n ON PORTx ANALOG INPUT/OUTPUT PIN n ON PORTx Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, SLEEP, and PUD are common to all ports. All other signals are unique for each pin. DATA BUS 61 7753C-AVR-07/09 Table 12-2 summarizes the function of the overriding signals. The pin and port indexes from Figure 12-5 are not shown in the succeeding tables. The overriding signals are generated internally in the modules having the alternate function. Table 12-2. Signal Name PUOE Generic Description of Overriding Signals for Alternate Functions Full Name Pull-up Override Enable Pull-up Override Value Data Direction Override Enable Data Direction Override Value Description If this signal is set, the pull-up enable is controlled by the PUOV signal. If this signal is cleared, the pull-up is enabled when {DDxn, PORTxn, PUD} = 0b010. If PUOE is set, the pull-up is enabled/disabled when PUOV is set/cleared, regardless of the setting of the DDxn, PORTxn, and PUD Register bits. If this signal is set, the Output Driver Enable is controlled by the DDOV signal. If this signal is cleared, the Output driver is enabled by the DDxn Register bit. If DDOE is set, the Output Driver is enabled/disabled when DDOV is set/cleared, regardless of the setting of the DDxn Register bit. If this signal is set and the Output Driver is enabled, the port value is controlled by the PVOV signal. If PVOE is cleared, and the Output Driver is enabled, the port Value is controlled by the PORTxn Register bit. If PVOE is set, the port value is set to PVOV, regardless of the setting of the PORTxn Register bit. If PTOE is set, the PORTxn Register bit is inverted. If this bit is set, the Digital Input Enable is controlled by the DIEOV signal. If this signal is cleared, the Digital Input Enable is determined by MCU state (Normal mode, sleep mode). If DIEOE is set, the Digital Input is enabled/disabled when DIEOV is set/cleared, regardless of the MCU state (Normal mode, sleep mode). This is the Digital Input to alternate functions. In the figure, the signal is connected to the output of the schmitt-trigger but before the synchronizer. Unless the Digital Input is used as a clock source, the module with the alternate function will use its own synchronizer. This is the Analog Input/Output to/from alternate functions. The signal is connected directly to the pad, and can be used bi-directionally. PUOV DDOE DDOV PVOE Port Value Override Enable Port Value Override Value Port Toggle Override Enable Digital Input Enable Override Enable Digital Input Enable Override Value PVOV PTOE DIEOE DIEOV DI Digital Input AIO Analog Input/Output The following subsections shortly describe the alternate functions for each port, and relate the overriding signals to the alternate function. Refer to the alternate function description for further details. 62 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 12.3.1 Alternate Functions of Port B The Port B pins with alternate function are shown in Table 12-3. Table 12-3. Port B Pins Alternate Functions Alternate Function RESET / dW / ADC10 / PCINT15 ADC9 / T0 / INT0 / PCINT14 XTAL2 / CLKO / OC1D / ADC8 / PCINT13 XTAL1 / CLKI / OC1D / ADC7 / PCINT12 OC1B / PCINT11 SCK / USCK / SCL / OC1B /PCINT10 MISO / DO / OC1A / PCINT9 MOSI / DI / SDA / OC1A / PCINT8 Port Pin PB7 PB6 PB5 PB4 PB3 PB2 PB1 PB0 The alternate pin configuration is as follows: * Port B, Bit 7 - RESET/ dW/ ADC10/ PCINT15 RESET, Reset pin: When the RSTDISBL Fuse is programmed, this pin functions as a normal I/O pin, and the part will have to rely on Power-on Reset and Brown-out Reset as its reset sources. When the RSTDISBL Fuse is unprogrammed, the reset circuitry is connected to the pin, and the pin can not be used as an I/O pin. If PB7 is used as a reset pin, DDB7, PORTB7 and PINB7 will all read 0. dW: When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unprogrammed, the RESET port pin is configured as a wire-AND (open-drain) bi-directional I/O pin with pull-up enabled and becomes the communication gateway between target and emulator. ADC10: ADC input Channel 10. Note that ADC input channel 10 uses analog power. PCINT15: Pin Change Interrupt source 15. * Port B, Bit 6 - ADC9/ T0/ INT0/ PCINT14 ADC9: ADC input Channel 9. Note that ADC input channel 9 uses analog power. T0: Timer/Counter0 counter source. INT0: The PB6 pin can serve as an External Interrupt source 0. PCINT14: Pin Change Interrupt source 14. * Port B, Bit 5 - XTAL2/ CLKO/ ADC8/ PCINT13 XTAL2: Chip clock Oscillator pin 2. Used as clock pin for crystal Oscillator or Low-frequency crystal Oscillator. When used as a clock pin, the pin can not be used as an I/O pin. CLKO: The divided system clock can be output on the PB5 pin, if the CKOUT Fuse is programmed, regardless of the PORTB5 and DDB5 settings. It will also be output during reset. OC1D Output Compare Match output: The PB5 pin can serve as an external output for the Timer/Counter1 Compare Match D when configured as an output (DDA1 set). The OC1D pin is also the output pin for the PWM mode timer function. 63 7753C-AVR-07/09 ADC8: ADC input Channel 8. Note that ADC input channel 8 uses analog power. PCINT13: Pin Change Interrupt source 13. * Port B, Bit 4 - XTAL1/ CLKI/ OC1B/ ADC7/ PCINT12 XTAL1/CLKI: Chip clock Oscillator pin 1. Used for all chip clock sources except internal calibrated RC Oscillator. When used as a clock pin, the pin can not be used as an I/O pin. OC1D: Inverted Output Compare Match output: The PB4 pin can serve as an external output for the Timer/Counter1 Compare Match D when configured as an output (DDA0 set). The OC1D pin is also the inverted output pin for the PWM mode timer function. ADC7: ADC input Channel 7. Note that ADC input channel 7 uses analog power. PCINT12: Pin Change Interrupt source 12. * Port B, Bit 3 - OC1B/ PCINT11 OC1B, Output Compare Match output: The PB3 pin can serve as an external output for the Timer/Counter1 Compare Match B. The PB3 pin has to be configured as an output (DDB3 set (one)) to serve this function. The OC1B pin is also the output pin for the PWM mode timer function. PCINT11: Pin Change Interrupt source 11. * Port B, Bit 2 - SCK/ USCK/ SCL/ OC1B/ PCINT10 SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB2. When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB2. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB2 bit. USCK: Three-wire mode Universal Serial Interface Clock. SCL: Two-wire mode Serial Clock for USI Two-wire mode. OC1B: Inverted Output Compare Match output: The PB2 pin can serve as an external output for the Timer/Counter1 Compare Match B when configured as an output (DDB2 set). The OC1B pin is also the inverted output pin for the PWM mode timer function. PCINT10: Pin Change Interrupt source 10. * Port B, Bit 1 - MISO/ DO/ OC1A/ PCINT9 MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is enabled as a Master, this pin is configured as an input regardless of the setting of DDB1. When the SPI is enabled as a Slave, the data direction of this pin is controlled by DDB1. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB1 bit. DO: Three-wire mode Universal Serial Interface Data output. Three-wire mode Data output overrides PORTB1 value and it is driven to the port when data direction bit DDB1 is set (one). PORTB1 still enables the pull-up, if the direction is input and PORTB1 is set (one). OC1A: Output Compare Match output: The PB1 pin can serve as an external output for the Timer/Counter1 Compare Match B when configured as an output (DDB1 set). The OC1A pin is also the output pin for the PWM mode timer function. PCINT9: Pin Change Interrupt source 9. 64 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 * Port B, Bit 0 - MOSI/ DI/ SDA/ OC1A/ PCINT8 MOSI: SPI Master Data output, Slave Data input for SPI channel. When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB0. When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB0. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB0 bit. DI: Data Input in USI Three-wire mode. USI Three-wire mode does not override normal port functions, so pin must be configure as an input for DI function. SDA: Two-wire mode Serial Interface Data. OC1A: Inverted Output Compare Match output: The PB0 pin can serve as an external output for the Timer/Counter1 Compare Match B when configured as an output (DDB0 set). The OC1A pin is also the inverted output pin for the PWM mode timer function. PCINT8: Pin Change Interrupt source 8. Table 12-4 and Table 12-5 relate the alternate functions of Port B to the overriding signals shown in Figure 12-5 on page 61. Table 12-4. Signal Name PUOE PUOV DDOE DDOV PVOE PVOV PTOE DIEOE DIEOV DI AIO Note: Overriding Signals for Alternate Functions in PB7..PB4 PB6/ADC9/T0/INT0/ PCINT14 0 0 0 PB5/XTAL2/CLKO/ OC1D/ADC8/PCINT13(1) INTRC * EXTCLK 0 INTRC * EXTCLK 0 OC1D Enable OC1D 0 PB4/XTAL1/OC1D/ ADC7/PCINT12(1) INTRC 0 INTRC 0 OC1D Enable OC1D 0 PB7/RESET/dW/ ADC10/PCINT15 RSTDISBL(1) * DWEN(1) 1 RSTDISBL(1) * DWEN(1) debugWire Transmit 0 0 0 0 0 ADC10D PCINT15 RESET / ADC10 0 0 0 RSTDISBL + (PCINT5 INTRC * EXTCLK + PCINT4 * INTRC + PCINT12 * PCIE + ADC9D) PCIE + ADC8D * PCIE + ADC7D ADC9D T0/INT0/PCINT14 ADC9 (INTRC * EXTCLK) + ADC8D INTRC * ADC7D PCINT13 XTAL2, ADC8 PCINT12 XTAL1, ADC7 1. 1 when the Fuse is "0" (Programmed). 65 7753C-AVR-07/09 Table 12-5. Signal Name PUOE PUOV DDOE DDOV Overriding Signals for Alternate Functions in PB3..PB0 PB2/SCK/USCK/SCL/ OC1B/PCINT10 0 0 USI_TWO_WIRE * USIPOS (USI_SCL_HOLD + PORTB2) * DDB2 * USIPOS OC1B Enable + USIPOS * USI_TWO_WIRE * DDB2 OC1B USITC * USIPOS PCINT10 * PCIE + USISIE * USIPOS 0 USCK/SCL/PCINT10 PB1/MISO/DO/OC1A/ PCINT9 0 0 0 0 PB0/MOSI/DI/SDA/ OC1A/PCINT8 0 0 USI_TWO_WIRE * USIPOS (SDA + PORTB0) * DDB0 * USIPOS PB3/OC1B/ PCINT11 0 0 0 0 PVOE PVOV PTOE OC1B Enable OC1B 0 OC1A Enable + OC1A Enable + USIPOS (USI_TWO_WIRE * * USI_THREE_WIRE DDB0 * USIPOS) OC1A + (DO * USIPOS) 0 PCINT9 * PCIE 0 PCINT9 OC1A 0 PCINT8 * PCIE + (USISIE * USIPOS) 0 DI/SDA/PCINT8 DIEOE PCINT11 * PCIE DIEOV 0 DI AIO Note: PCINT11 1. INTRC means that one of the internal RC Oscillators are selected (by the CKSEL fuses), EXTCK means that external clock is selected (by the CKSEL fuses). 12.3.2 Alternate Functions of Port A The Port A pins with alternate function are shown in Table 12-6. Table 12-6. Port B Pins Alternate Functions Alternate Function ADC6 / AIN0 / PCINT7 ADC5 / AIN1 / PCINT6 ADC4 / AIN2 / PCINT5 ADC3 /ICP0/ PCINT4 AREF / PCINT3 ADC2 / INT1 / USCK / SCL / PCINT2 ADC1 / DO / PCINT1 ADC0 / DI / SDA / PCINT0 Port Pin PA7 PA6 PA5 PA4 PA3 PA2 PA1 PA0 The alternate pin configuration is as follows: * Port A, Bit 7- ADC6/AIN0/PCINT7 ADC6: Analog to Digital Converter, Channel 6. AIN0: Analog Comparator Input. Configure the port pin as input with the internal pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator. PCINT7: Pin Change Interrupt source 8. 66 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 * Port A, Bit 6 - ADC5/AIN1/PCINT6 ADC5: Analog to Digital Converter, Channel 5. AIN1: Analog Comparator Input. Configure the port pin as input with the internal pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator. PCINT6: Pin Change Interrupt source 6. * Port A, Bit 5 - ADC4/AIN2/PCINT5 ADC4: Analog to Digital Converter, Channel 4. AIN2: Analog Comparator Input. Configure the port pin as input with the internal pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator. PCINT5: Pin Change Interrupt source 5. * Port A, Bit 4 - ADC3/ICP0/PCINT4 ADC3: Analog to Digital Converter, Channel 3. ICP0: Timer/Counter0 Input Capture Pin. PCINT4: Pin Change Interrupt source 4. * Port A, Bit 3 - AREF/PCINT3 AREF: External analog reference for ADC. Pull-up and output driver are disabled on PA3 when the pin is used as an external reference or internal voltage reference with external capacitor at the AREF pin. PCINT3: Pin Change Interrupt source 3. * Port A, Bit 2 - ADC2/INT1/USCK/SCL/PCINT2 ADC2: Analog to Digital Converter, Channel 2. INT1: The PA2 pin can serve as an External Interrupt source 1. USCK: Three-wire mode Universal Serial Interface Clock. SCL: Two-wire mode Serial Clock for USI Two-wire mode. PCINT2: Pin Change Interrupt source 2. * Port A, Bit 1 - ADC1/DO/PCINT1 ADC1: Analog to Digital Converter, Channel 1. DO: Three-wire mode Universal Serial Interface Data output. Three-wire mode Data output overrides PORTA1 value and it is driven to the port when data direction bit DDA1 is set. PORTA1 still enables the pull-up, if the direction is input and PORTA1 is set. PCINT1: Pin Change Interrupt source 1. * Port A, Bit 0 - ADC0/DI/SDA/PCINT0 ADC0: Analog to Digital Converter, Channel 0. 67 7753C-AVR-07/09 DI: Data Input in USI Three-wire mode. USI Three-wire mode does not override normal port functions, so pin must be configure as an input for DI function. SDA: Two-wire mode Serial Interface Data. PCINT0: Pin Change Interrupt source 0. Table 12-7 and Table 12-8 relate the alternate functions of Port A to the overriding signals shown in Figure 12-5 on page 61. Table 12-7. Signal Name PUOE PUOV DDOE DDOV PVOE PVOV PTOE DIEOE DIEOV DI AIO Overriding Signals for Alternate Functions in PA7..PA4 PA7/ADC6/AIN0/ PCINT7 0 0 0 0 0 0 0 PCINT7 * PCIE + ADC6D ADC6D PCINT7 ADC6, AIN0 PA6/ADC5/AIN1/ PCINT6 0 0 0 0 0 0 0 PCINT6 * PCIE + ADC5D ADC5D PCINT6 ADC5, AIN1 PA5/ADC4/AIN2/ PCINT5 0 0 0 0 0 0 0 PCINT5 * PCIE + ADC4D ADC4D PCINT5 ADC4, AIN2 PA4/ADC3/ICP0/ PCINT4 0 0 0 0 0 0 0 PCINT4 * PCIE + ADC3D ADC3D ICP0/PCINT4 ADC3 Table 12-8. Signal Name PUOE PUOV DDOE DDOV PVOE PVOV PTOE DIEOE DIEOV DI AIO Overriding Signals for Alternate Functions in PA3..PA0 PA3/AREF/ PCINT3 0 0 0 0 0 0 0 PA2/ADC2/INT1/ USCK/SCL/PCINT2 0 0 USI_TWO_WIRE * USIPOS PA1/ADC1/DO/ PCINT1 0 0 0 PA0/ADC0/DI/SDA/ PCINT0 0 0 USI_TWO_WIRE * USIPOS (SDA + PORTB0) * DDRB0 * USIPOS (USI_SCL_HOLD + 0 PORTB2) * DDB2 * USIPOS USI_TWO_WIRE * DDRB2 0 USI_PTOE * USIPOS USI_THREE_WIRE USI_TWO_WIRE * * USIPOS DDRB0 * USIPOS DO * USIPOS 0 0 0 PCINT0 * PCIE + ADC0D + USISIE * USIPOS ADC0D DI/SDA/PCINT0 ADC0 PCINT3 * PCIE PCINT2 * PCIE + INT1 + PCINT1 * PCIE + ADC2D + USISIE * USIPOS ADC1D 0 PCINT3 AREF ADC2D USCK/SCL/INT1/ PCINT2 ADC2 ADC1D PCINT1 ADC1 68 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 12.4 12.4.1 Register Description MCUCR - MCU Control Register Bit 0x35 (0x55) Read/Write Initial Value 7 R 0 6 PUD R/W 0 5 SE R/W 0 4 SM1 R/W 0 3 SM0 R/W 0 2 R 0 1 ISC01 R 0 0 ISC00 R 0 MCUCR * Bit 6 - PUD: Pull-up Disable When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See "Configuring the Pin" on page 56 for more details about this feature. 12.4.2 PORTA - Port A Data Register Bit 0x1B (0x3B) Read/Write Initial Value 7 PORTA7 R/W 0 6 PORTA6 R/W 0 5 PORTA5 R/W 0 4 PORTA4 R/W 0 3 PORTA3 R/W 0 2 PORTA2 R/W 0 1 PORTA1 R/W 0 0 PORTA0 R/W 0 PORTA 12.4.3 DDRA - Port A Data Direction Register Bit 0x1A (0x3A) Read/Write Initial Value 7 DDA7 R/W 0 6 DDA6 R/W 0 5 DDA5 R/W 0 4 DDA4 R/W 0 3 DDA3 R/W 0 2 DDA2 R/W 0 1 DDA1 R/W 0 0 DDA0 R/W 0 DDRA 12.4.4 PINA - Port A Input Pins Address Bit 0x19 (0x39) Read/Write Initial Value 7 PINA7 R/W N/A 6 PINA6 R/W N/A 5 PINA5 R/W N/A 4 PINA4 R/W N/A 3 PINA3 R/W N/A 2 PINA2 R/W N/A 1 PINA1 R/W N/A 0 PINA0 R/W N/A PINA 12.4.5 PORTB - Port B Data Register Bit 0x18 (0x38) Read/Write Initial Value 7 PORTB7 R/W 0 6 PORTB6 R/W 0 5 PORTB5 R/W 0 4 PORTB4 R/W 0 3 PORTB3 R/W 0 2 PORTB2 R/W 0 1 PORTB1 R/W 0 0 PORTB0 R/W 0 PORTB 12.4.6 DDRB - Port B Data Direction Register Bit 0x17 (0x37) Read/Write Initial Value 7 DDB7 R/W 0 6 DDB6 R/W 0 5 DDB5 R/W 0 4 DDB4 R/W 0 3 DDB3 R/W 0 2 DDB2 R/W 0 1 DDB1 R/W 0 0 DDB0 R/W 0 DDRB 12.4.7 PINB - Port B Input Pins Address Bit 0x16 (0x36) Read/Write Initial Value 7 PINB7 R/W N/A 6 PINB6 R/W N/A 5 PINB5 R/W N/A 4 PINB4 R/W N/A 3 PINB3 R/W N/A 2 PINB2 R/W N/A 1 PINB1 R/W N/A 0 PINB0 R/W N/A PINB 69 7753C-AVR-07/09 13. Timer/Counter0 Prescaler The Timer/Counter can be clocked directly by the system clock (by setting the CSn2:0 = 1). This provides the fastest operation, with a maximum Timer/Counter clock frequency equal to system clock frequency (fCLK_I/O). Alternatively, one of four taps from the prescaler can be used as a clock source. The prescaled clock has a frequency of either fCLK_I/O/8, fCLK_I/O/64, fCLK_I/O/256, or fCLK_I/O/1024. See Table 13-1 on page 72 for details. 13.0.1 Prescaler Reset The prescaler is free running, i.e., operates independently of the Clock Select logic of the Timer/Counter. Since the prescaler is not affected by the Timer/Counter's clock select, the state of the prescaler will have implications for situations where a prescaled clock is used. One example of prescaling artifacts occurs when the timer is enabled and clocked by the prescaler (6 > CSn2:0 > 1). The number of system clock cycles from when the timer is enabled to the first count occurs can be from 1 to N+1 system clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024). It is possible to use the Prescaler Reset for synchronizing the Timer/Counter to program execution. External Clock Source An external clock source applied to the T0 pin can be used as Timer/Counter clock (clkT0). The T0 pin is sampled once every system clock cycle by the pin synchronization logic. The synchronized (sampled) signal is then passed through the edge detector. Figure 13-1 shows a functional equivalent block diagram of the T0 synchronization and edge detector logic. The registers are clocked at the positive edge of the internal system clock (clkI/O). The latch is transparent in the high period of the internal system clock. The edge detector generates one clkT0 pulse for each positive (CSn2:0 = 7) or negative (CSn2:0 = 6) edge it detects. See Table 13-1 on page 72 for details. Figure 13-1. T0 Pin Sampling 13.0.2 Tn D LE Q D Q D Q Tn_sync (To Clock Select Logic) clk I/O Synchronization Edge Detector The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles from an edge has been applied to the T0 pin to the counter is updated. Enabling and disabling of the clock input must be done when T0 has been stable for at least one system clock cycle, otherwise it is a risk that a false Timer/Counter clock pulse is generated. Each half period of the external clock applied must be longer than one system clock cycle to ensure correct sampling. The external clock must be guaranteed to have less than half the system clock frequency (fExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since the edge detector uses sampling, the maximum frequency of an external clock it can detect is half the sampling frequency (Nyquist sampling theorem). 70 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 However, due to variation of the system clock frequency and duty cycle caused by Oscillator source (crystal, resonator, and capacitors) tolerances, it is recommended that maximum frequency of an external clock source is less than fclk_I/O/2.5. An external clock source can not be prescaled. Figure 13-2. Prescaler for Timer/Counter0 clk I/O Clear PSR0 T0 Synchronization clkT0 Note: 1. The synchronization logic on the input pins (T0) is shown in Figure 13-1. 13.1 13.1.1 Register Description TCCR0B - Timer/Counter0 Control Register B Bit 0x33 (0x53) Read/Write Initial Value 7 R 0 6 R 0 5 R 0 4 TSM R/W 0 3 PSR0 R/W 0 2 CS02 R/W 0 1 CS01 R/W 0 0 CS01 R/W 0 TCCR0B * Bit 4 - TSM: Timer/Counter Synchronization Mode Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this mode, the value that is written to the PSR0 bit is kept, hence keeping the Prescaler Reset signal asserted. This ensures that the Timer/Counter is halted and can be configured without the risk of advancing during configuration. When the TSM bit is written to zero, the PSR0 bit is cleared by hardware, and the Timer/Counter start counting. * Bit 3 - PSR0: Prescaler Reset Timer/Counter0 When this bit is one, the Timer/Counter0 prescaler will be Reset. This bit is normally cleared immediately by hardware, except if the TSM bit is set. * Bits 2, 1, 0 - CS02, CS01, CS00: Clock Select0, Bit 2, 1, and 0 The Clock Select0 bits 2, 1, and 0 define the prescaling source of Timer0. 71 7753C-AVR-07/09 Table 13-1. CS02 0 0 0 0 1 1 1 1 Clock Select Bit Description CS01 0 0 1 1 0 0 1 1 CS00 0 1 0 1 0 1 0 1 Description No clock source (Timer/Counter stopped) clkI/O/(No prescaling) clkI/O/8 (From prescaler) clkI/O/64 (From prescaler) clkI/O/256 (From prescaler) clkI/O/1024 (From prescaler) External clock source on T0 pin. Clock on falling edge. External clock source on T0 pin. Clock on rising edge. If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the counter even if the pin is configured as an output. This feature allows software control of the counting. 72 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 14. Timer/Counter0 14.1 Features * * * * * Clear Timer on Compare Match (Auto Reload) Input Capture unit Four Independent Interrupt Sources (TOV0, OCF0A, OCF0B, ICF0) 8-bit Mode with Two Independent Output Compare Units 16-bit Mode with One Independent Output Compare Unit 14.2 Overview Timer/Counter0 is a general purpose 8-/16-bit Timer/Counter module, with two/one Output Compare units and Input Capture feature. The Timer/Counter0 general operation is described in 8-/16-bit mode. A simplified block diagram of the 8-/16-bit Timer/Counter is shown in Figure 14-1. For the actual placement of I/O pins, refer to "Pinout ATtiny261/461/861" on page 2. CPU accessible I/O Registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed in the "Register Description" on page 85. Figure 14-1. 8-/16-bit Timer/Counter Block Diagram TOVn (Int. Req.) Count Clear Direction clkTn Control Logic Clock Select Edge Detector ( From Prescaler ) Timer/Counter TCNTnH TCNTnL TOP Tn = Fixed TOP value OCnA (Int. Req.) OCnB (Int. Req.) = = DATA BUS ICFn (Int. Req.) OCRnB OCRnA ( From Analog Comparator Ouput ) TCCRnA TCCRnB Edge Detector Noise Canceler ICPn 14.2.1 Registers The Timer/Counter0 Low Byte Register (TCNT0L) and Output Compare Registers (OCR0A and OCR0B) are 8-bit registers. Interrupt request (abbreviated to Int.Req. in Figure 14-1) signals are all visible in the Timer Interrupt Flag Register (TIFR). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK). TIFR and TIMSK are not shown in the figure. In 16-bit mode the Timer/Counter consists one more 8-bit register, the Timer/Counter0 High Byte Register (TCNT0H). Furthermore, there is only one Output Compare Unit in 16-bit mode as the two Output Compare Registers, OCR0A and OCR0B, are combined to one 16-bit Output Compare Register. 73 7753C-AVR-07/09 OCR0A contains the low byte of the word and OCR0B contains the high byte of the word. When accessing 16-bit registers, special procedures described in section "Accessing Registers in 16-bit Mode" on page 81 must be followed. 14.2.2 Definitions Many register and bit references in this section are written in general form. A lower case "n" replaces the Timer/Counter number, in this case 0. A lower case "x" replaces the Output Compare Unit, in this case Compare Unit A or Compare Unit B. However, when using the register or bit defines in a program, the precise form must be used, i.e., TCNT0L for accessing Timer/Counter0 counter value and so on. The definitions in Table 14-1 are also used extensively throughout the document. Table 14-1. BOTTOM MAX Definitions The counter reaches the BOTTOM when it becomes 0. The counter reaches its MAXimum when it becomes 0xFF (decimal 255) in 8-bit mode or 0xFFFF (decimal 65535) in 16-bit mode. The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The TOP value can be assigned to be the fixed value 0xFF/0xFFFF (MAX) or the value stored in the OCR0A Register. TOP 14.3 Timer/Counter Clock Sources The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on the T0 pin. The Clock Select logic is controlled by the Clock Select (CS02:0) bits located in the Timer/Counter Control Register 0 B (TCCR0B), and controls which clock source and edge the Timer/Counter uses to increment its value. The Timer/Counter is inactive when no clock source is selected. The output from the Clock Select logic is referred to as the timer clock (clkT0). For details on clock sources and prescaler, see "Timer/Counter0 Prescaler" on page 70. 14.4 Counter Unit The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure 14-3 shows a block diagram of the counter and its surroundings. Table 14-2. Counter Unit Block Diagram DATA BUS TOVn (Int.Req.) Clock Select Edge Detector Tn TCNTn count Control Logic clkTn ( From Prescaler ) top Signal description (internal signals): count clkTn top Increment or decrement TCNT0 by 1. Timer/Counter clock, referred to as clkT0 in the following. Signalize that TCNT0 has reached maximum value. 74 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 The counter is incremented at each timer clock (clkT0) until it passes its TOP value and then restarts from BOTTOM. The counting sequence is determined by the setting of the CTC0 bit located in the Timer/Counter Control Register (TCCR0A). For more details about counting sequences, see "Modes of Operation" on page 75. clkT0 can be generated from an external or internal clock source, selected by the Clock Select bits (CS02:0). When no clock source is selected (CS02:0 = 0) the timer is stopped. However, the TCNT0 value can be accessed by the CPU, regardless of whether clkT0 is present or not. A CPU write overrides (has priority over) all counter clear or count operations. The Timer/Counter Overflow Flag (TOV0) is set when the counter reaches the maximum value and it can be used for generating a CPU interrupt. 14.5 Modes of Operation The mode of operation is defined by the Timer/Counter Width (TCW0), Input Capture Enable (ICEN0) and Wave Generation Mode (CTC0) bits in "TCCR0A - Timer/Counter0 Control Register A" on page 85. Table 14-3 shows the different Modes of Operation. Table 14-3. Mode 0 1 2 3 4 Modes of operation ICEN0 0 0 0 1 1 TCW0 0 0 1 0 1 CTC0 0 1 X X X Mode of Operation Normal 8-bit Mode 8-bit CTC 16-bit Mode 8-bit Input Capture Mode 16-bit Input Capture Mode TOP Value 0xFF OCR0A 0xFFFF 0xFF 0xFFFF Update of OCRx at Immediate Immediate Immediate Immediate Immediate TOV Flag Set on MAX (0xFF) MAX (0xFF) MAX (0xFFFF) MAX (0xFF) MAX (0xFFFF) 14.5.1 Normal 8-bit Mode In the Normal 8-bit mode, see Table 14-3 on page 75, the counter (TCNT0L) is incrementing until it overruns when it passes its maximum 8-bit value (MAX = 0xFF) and then restarts from the bottom (0x00). The Overflow Flag (TOV0) will be set in the same timer clock cycle as the TCNT0L becomes zero. The TOV0 Flag in this case behaves like a ninth bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOV0 Flag, the timer resolution can be increased by software. There are no special cases to consider in the Normal 8-bit mode, a new counter value can be written anytime. The Output Compare Unit can be used to generate interrupts at some given time. Clear Timer on Compare Match (CTC) 8-bit Mode In Clear Timer on Compare or CTC mode, see Table 14-3 on page 75, the OCR0A Register is used to manipulate the counter resolution. In CTC mode the counter is cleared to zero when the counter value (TCNT0) matches the OCR0A. The OCR0A defines the top value for the counter, hence also its resolution. This mode allows greater control of the Compare Match output frequency. It also simplifies the operation of counting external events. The timing diagram for the CTC mode is shown in Figure 14-2. The counter value (TCNT0) increases until a Compare Match occurs between TCNT0 and OCR0A, and then counter (TCNT0) is cleared. 14.5.2 75 7753C-AVR-07/09 Figure 14-2. CTC Mode, Timing Diagram OCnx Interrupt Flag Set TCNTn Period 1 2 3 4 An interrupt can be generated each time the counter value reaches the TOP value by using the OCF0A Flag. If the interrupt is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing TOP to a value close to BOTTOM when the counter is running with none or a low prescaler value must be done with care since the CTC mode does not have the double buffering feature. If the new value written to OCR0A is lower than the current value of TCNT0, the counter will miss the Compare Match. The counter will then have to count to its maximum value (0xFF) and wrap around starting at 0x00 before the Compare Match can occur. As for the Normal mode of operation, the TOV0 Flag is set in the same timer clock cycle that the counter counts from MAX to 0x00. 14.5.3 16-bit Mode In 16-bit mode, see Table 14-3 on page 75, the counter (TCNT0H/L) is a incrementing until it overruns when it passes its maximum 16-bit value (MAX = 0xFFFF) and then restarts from the bottom (0x0000). The Overflow Flag (TOV0) will be set in the same timer clock cycle as the TCNT0H/L becomes zero. The TOV0 Flag in this case behaves like a 17th bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOV0 Flag, the timer resolution can be increased by software. There are no special cases to consider in the Normal mode, a new counter value can be written anytime. The Output Compare Unit can be used to generate interrupts at some given time. 14.5.4 8-bit Input Capture Mode The Timer/Counter0 can also be used in an 8-bit Input Capture mode, see Table 14-3 on page 75 for bit settings. For full description, see the section "Input Capture Unit" on page 77. 16-bit Input Capture Mode The Timer/Counter0 can also be used in a 16-bit Input Capture mode, see Table 14-3 on page 75 for bit settings. For full description, see the section "Input Capture Unit" on page 77. 14.5.5 76 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 14.6 Input Capture Unit The Timer/Counter incorporates an Input Capture unit that can capture external events and give them a time-stamp indicating time of occurrence. The external signal indicating an event, or multiple events, can be applied via the ICP0 pin or alternatively, via the analog-comparator unit. The time-stamps can then be used to calculate frequency, duty-cycle, and other features of the signal applied. Alternatively the time-stamps can be used for creating a log of the events. The Input Capture unit is illustrated by the block diagram shown in Figure 14-3. The elements of the block diagram that are not directly a part of the Input Capture unit are gray shaded. Figure 14-3. Input Capture Unit Block Diagram DATA BUS (8-bit) TEMP (8-bit) OCR0B (8-bit) WRITE OCR0A (8-bit) TCNT0H (8-bit) TCNT0L (8-bit) ICR0 (16-bit Register) TCNT0 (16-bit Counter) ACO* Analog Comparator ICP0 ACIC0* ICNC0 ICES0 Noise Canceler Edge Detector ICF0 (Int.Req.) The Output Compare Register OCR0A is a dual-purpose register that is also used as an 8-bit Input Capture Register ICR0. In 16-bit Input Capture mode the Output Compare Register OCR0B serves as the high byte of the Input Capture Register ICR0. In 8-bit Input Capture mode the Output Compare Register OCR0B is free to be used as a normal Output Compare Register, but in 16-bit Input Capture mode the Output Compare Unit cannot be used as there are no free Output Compare Register(s). Even though the Input Capture register is called ICR0 in this section, it is referring to the Output Compare Register(s). When a change of the logic level (an event) occurs on the Input Capture pin (ICP0), alternatively on the Analog Comparator output (ACO), and this change confirms to the setting of the edge detector, a capture will be triggered. When a capture is triggered, the value of the counter (TCNT0) is written to the Input Capture Register (ICR0). The Input Capture Flag (ICF0) is set at the same system clock as the TCNT0 value is copied into Input Capture Register. If enabled (TICIE0=1), the Input Capture Flag generates an Input Capture interrupt. The ICF0 flag is automatically cleared when the interrupt is executed. Alternatively the ICF0 flag can be cleared by software by writing a logical one to its I/O bit location. 77 7753C-AVR-07/09 14.6.1 Input Capture Trigger Source The default trigger source for the Input Capture unit is the Input Capture pin (ICP0). Timer/Counter0 can alternatively use the Analog Comparator output as trigger source for the Input Capture unit. The Analog Comparator is selected as trigger source by setting the Analog Comparator Input Capture Enable (ACIC0) bit in the Timer/Counter Control Register A (TCCR0A). Be aware that changing trigger source can trigger a capture. The Input Capture Flag must therefore be cleared after the change. Both the Input Capture pin (ICP0) and the Analog Comparator output (ACO) inputs are sampled using the same technique as for the T0 pin (Figure 13-1 on page 72). The edge detector is also identical. However, when the noise canceler is enabled, additional logic is inserted before the edge detector, which increases the delay by four system clock cycles. An Input Capture can also be triggered by software by controlling the port of the ICP0 pin. 14.6.2 Noise Canceler The noise canceler improves noise immunity by using a simple digital filtering scheme. The noise canceler input is monitored over four samples, and all four must be equal for changing the output that in turn is used by the edge detector. The noise canceler is enabled by setting the Input Capture Noise Canceler (ICNC0) bit in Timer/Counter Control Register B (TCCR0B). When enabled the noise canceler introduces additional four system clock cycles of delay from a change applied to the input, to the update of the ICR0 Register. The noise canceler uses the system clock and is therefore not affected by the prescaler. 14.6.3 Using the Input Capture Unit The main challenge when using the Input Capture unit is to assign enough processor capacity for handling the incoming events. The time between two events is critical. If the processor has not read the captured value in the ICR0 Register before the next event occurs, the ICR0 will be overwritten with a new value. In this case the result of the capture will be incorrect. When using the Input Capture interrupt, the ICR0 Register should be read as early in the interrupt handler routine as possible. The maximum interrupt response time is dependent on the maximum number of clock cycles it takes to handle any of the other interrupt requests. Measurement of an external signal's duty cycle requires that the trigger edge is changed after each capture. Changing the edge sensing must be done as early as possible after the ICR0 Register has been read. After a change of the edge, the Input Capture Flag (ICF0) must be cleared by software (writing a logical one to the I/O bit location). For measuring frequency only, the trigger edge change is not required (if an interrupt handler is used). 14.7 Output Compare Unit The comparator continuously compares Timer/Counter (TCNT0) with the Output Compare Registers (OCR0A and OCR0B), and whenever the Timer/Counter equals to the Output Compare Registers, the comparator signals a match. A match will set the Output Compare Flag at the next timer clock cycle. In 8-bit mode the match can set either the Output Compare Flag OCF0A or OCF0B, but in 16-bit mode the match can set only the Output Compare Flag OCF0A as there is only one Output Compare Unit. If the corresponding interrupt is enabled, the Output Compare Flag generates an Output Compare interrupt. The Output Compare Flag is automatically cleared when the interrupt is executed. 78 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Alternatively, the flag can be cleared by software by writing a logical one to its I/O bit location. Figure 14-4 shows a block diagram of the Output Compare unit. Figure 14-4. Output Compare Unit, Block Diagram DATA BUS OCRnx TCNTn = (8/16-bit Comparator ) OCFnx (Int.Req.) 14.7.1 Compare Match Blocking by TCNT0 Write All CPU write operations to the TCNT0H/L Register will block any Compare Match that occur in the next timer clock cycle, even when the timer is stopped. This feature allows OCR0A/B to be initialized to the same value as TCNT0 without triggering an interrupt when the Timer/Counter clock is enabled. Using the Output Compare Unit Since writing TCNT0H/L will block all Compare Matches for one timer clock cycle, there are risks involved when changing TCNT0H/L when using the Output Compare Unit, independently of whether the Timer/Counter is running or not. If the value written to TCNT0H/L equals the OCR0A/B value, the Compare Match will be missed. 14.7.2 14.8 Timer/Counter Timing Diagrams The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore shown as a clock enable signal in the following figures. The figures include information on when Interrupt Flags are set. Figure 14-5 contains timing data for basic Timer/Counter operation. The figure shows the count sequence close to the MAX value. Figure 14-5. Timer/Counter Timing Diagram, no Prescaling clkI/O clkTn (clkI/O /1) TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1 TOVn Figure 14-6 shows the same timing data, but with the prescaler enabled. 79 7753C-AVR-07/09 Figure 14-6. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8) clkI/O clkTn (clkI/O /8) TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1 TOVn Figure 14-7 shows the setting of OCF0A and OCF0B in Normal mode. Figure 14-7. Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8) clkI/O clkTn (clkI/O /8) TCNTn OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2 OCRnx OCRnx Value OCFnx shows the setting of OCF0A and the clearing of TCNT0 in CTC mode. Figure 14-8. Timer/Counter Timing Diagram, CTC mode, with Prescaler (fclk_I/O/8) clkPCK clkTn (clkPCK /8) TCNTn (CTC) OCRnx TOP - 1 TOP BOTTOM BOTTOM + 1 TOP OCFnx 80 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 14.9 Accessing Registers in 16-bit Mode In 16-bit mode (the TCW0 bit is set to one) the TCNT0H/L and OCR0A/B or TCNT0L/H and OCR0B/A are 16-bit registers that can be accessed by the AVR CPU via the 8-bit data bus. The 16-bit register must be byte accessed using two read or write operations. The 16-bit Timer/Counter has a single 8-bit register for temporary storing of the high byte of the 16-bit access. The same temporary register is shared between all 16-bit registers. Accessing the low byte triggers the 16-bit read or write operation. When the low byte of a 16-bit register is written by the CPU, the high byte stored in the temporary register, and the low byte written are both copied into the 16-bit register in the same clock cycle. When the low byte of a 16-bit register is read by the CPU, the high byte of the 16-bit register is copied into the temporary register in the same clock cycle as the low byte is read. There is one exception in the temporary register usage. In the Output Compare mode the 16-bit Output Compare Register OCR0A/B is read without the temporary register, because the Output Compare Register contains a fixed value that is only changed by CPU access. However, in 16-bit Input Capture mode the ICR0 register formed by the OCR0A and OCR0B registers must be accessed with the temporary register. To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read, the low byte must be read before the high byte. 81 7753C-AVR-07/09 The following code examples show how to access the 16-bit timer registers assuming that no interrupts updates the temporary register. The same principle can be used directly for accessing the OCR0A/B registers. Assembly Code Example ... ; Set TCNT0 to 0x01FF ldi r17,0x01 ldi r16,0xFF out TCNT0H,r17 out TCNT0L,r16 ; Read TCNT0 into r17:r16 in r16,TCNT0L in r17,TCNT0H ... C Code Example unsigned int i; ... /* Set TCNT0 to 0x01FF */ TCNT0H = 0x01; TCNT0L = 0xff; /* Read TCNT0 into i */ i = TCNT0L; i |= ((unsigned int)TCNT0H << 8); ... Note: 1. The example code assumes that the part specific header file is included. For I/O registers located in extended I/O map, "IN", "OUT", "SBIS", "SBIC", "CBI", and "SBI" instructions must be replaced with instructions that allow access to extended I/O. Typically "LDS" and "STS" combined with "SBRS", "SBRC", "SBR", and "CBR". The assembly code example returns the TCNT0H/L value in the r17:r16 register pair. It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt occurs between the two instructions accessing the 16-bit register, and the interrupt code updates the temporary register by accessing the same or any other of the 16-bit timer registers, then the result of the access outside the interrupt will be corrupted. Therefore, when both the main code and the interrupt code update the temporary register, the main code must disable the interrupts during the 16-bit access. 82 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 The following code examples show how to do an atomic read of the TCNT0 register contents. Reading any of the OCR0 register can be done by using the same principle. Assembly Code Example TIM0_ReadTCNT0: ; Save global interrupt flag in r18,SREG ; Disable interrupts cli ; Read TCNT0 into r17:r16 in r16,TCNT0L in r17,TCNT0H ; Restore global interrupt flag out SREG,r18 ret C Code Example unsigned int TIM0_ReadTCNT0( void ) { unsigned char sreg; unsigned int i; /* Save global interrupt flag */ sreg = SREG; /* Disable interrupts */ _CLI(); /* Read TCNT0 into i */ i = TCNT0L; i |= ((unsigned int)TCNT0H << 8); /* Restore global interrupt flag */ SREG = sreg; return i; } Note: 1. The example code assumes that the part specific header file is included. For I/O registers located in extended I/O map, "IN", "OUT", "SBIS", "SBIC", "CBI", and "SBI" instructions must be replaced with instructions that allow access to extended I/O. Typically "LDS" and "STS" combined with "SBRS", "SBRC", "SBR", and "CBR". The assembly code example returns the TCNT0H/L value in the r17:r16 register pair. 83 7753C-AVR-07/09 The following code examples show how to do an atomic write of the TCNT0H/L register contents. Writing any of the OCR0A/B registers can be done by using the same principle. Assembly Code Example TIM0_WriteTCNT0: ; Save global interrupt flag in r18,SREG ; Disable interrupts cli ; Set TCNT0 to r17:r16 out TCNT0H,r17 out TCNT0L,r16 ; Restore global interrupt flag out SREG,r18 ret C Code Example void TIM0_WriteTCNT0( unsigned int i ) { unsigned char sreg; /* Save global interrupt flag */ sreg = SREG; /* Disable interrupts */ _CLI(); /* Set TCNT0 to i */ TCNT0H = (i >> 8); TCNT0L = (unsigned char)i; /* Restore global interrupt flag */ SREG = sreg; } Note: 1. The example code assumes that the part specific header file is included. For I/O registers located in extended I/O map, "IN", "OUT", "SBIS", "SBIC", "CBI", and "SBI" instructions must be replaced with instructions that allow access to extended I/O. Typically "LDS" and "STS" combined with "SBRS", "SBRC", "SBR", and "CBR". The assembly code example requires that the r17:r16 register pair contains the value to be written to TCNT0H/L. 14.9.1 Reusing the temporary high byte register If writing to more than one 16-bit register where the high byte is the same for all registers written, then the high byte only needs to be written once. However, note that the same rule of atomic operation described previously also applies in this case. 84 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 14.10 Register Description 14.10.1 TCCR0A - Timer/Counter0 Control Register A Bit 0x15 (0x35) Read/Write Initial Value 7 TCW0 6 ICEN0 5 ICNC0 4 ICES0 3 ACIC0 2 - 1 - 0 CTC0 TCCR0A R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R 0 R 0 R/W 0 * Bit 7- TCW0: Timer/Counter0 Width When this bit is written to one 16-bit mode is selected as described Figure 14-5 on page 79. Timer/Counter0 width is set to 16-bits and the Output Compare Registers OCR0A and OCR0B are combined to form one 16-bit Output Compare Register. Because the 16-bit registers TCNT0H/L and OCR0B/A are accessed by the AVR CPU via the 8-bit data bus, special procedures must be followed. These procedures are described in section "Accessing Registers in 16-bit Mode" on page 81. * Bit 6- ICEN0: Input Capture Mode Enable When this bit is written to one, the Input Capture Mode is enabled. * Bit 5 - ICNC0: Input Capture Noise Canceler Setting this bit activates the Input Capture Noise Canceler. When the noise canceler is activated, the input from the Input Capture Pin (ICP0) is filtered. The filter function requires four successive equal valued samples of the ICP0 pin for changing its output. The Input Capture is therefore delayed by four System Clock cycles when the noise canceler is enabled. * Bit 4 - ICES0: Input Capture Edge Select This bit selects which edge on the Input Capture Pin (ICP0) that is used to trigger a capture event. When the ICES0 bit is written to zero, a falling (negative) edge is used as trigger, and when the ICES0 bit is written to one, a rising (positive) edge will trigger the capture. When a capture is triggered according to the ICES0 setting, the counter value is copied into the Input Capture Register. The event will also set the Input Capture Flag (ICF0), and this can be used to cause an Input Capture Interrupt, if this interrupt is enabled. * Bit 3 - ACIC0: Analog Comparator Input Capture Enable When written logic one, this bit enables the input capture function in Timer/Counter0 to be triggered by the Analog Comparator. The comparator output is in this case directly connected to the input capture front-end logic, making the comparator utilize the noise canceler and edge select features of the Timer/Counter0 Input Capture interrupt. When written logic zero, no connection between the Analog Comparator and the input capture function exists. To make the comparator trigger the Timer/Counter0 Input Capture interrupt, the TICIE0 bit in the Timer Interrupt Mask Register (TIMSK) must be set. * Bits 2:1 - Res: Reserved Bits These bits are reserved bits in the ATtiny261/461/861 and will always read as zero. * Bit 0 - CTC0: Waveform Generation Mode This bit controls the counting sequence of the counter, the source for maximum (TOP) counter value, see Figure 14-5 on page 79. 85 7753C-AVR-07/09 Modes of operation supported by the Timer/Counter unit are: Normal mode (counter) and Clear Timer on Compare Match (CTC) mode (see "Modes of Operation" on page 75). 14.10.2 TCNT0L - Timer/Counter0 Register Low Byte Bit 0x32 (0x52) Read/Write Initial Value R/W 0 R/W 0 R/W 0 7 6 5 4 3 2 1 0 TCNT0L R/W 0 R/W 0 R/W 0 TCNT0L[7:0] R/W 0 R/W 0 The Timer/Counter0 Register Low Byte, TCNT0L, gives direct access, both for read and write operations, to the Timer/Counter unit 8-bit counter. Writing to the TCNT0L Register blocks (disables) the Compare Match on the following timer clock. Modifying the counter (TCNT0L) while the counter is running, introduces a risk of missing a Compare Match between TCNT0L and the OCR0x Registers. In 16-bit mode the TCNT0L register contains the lower part of the 16-bit Timer/Counter0 Register. 14.10.3 TCNT0H - Timer/Counter0 Register High Byte Bit 0x14 (0x34) Read/Write Initial Value R/W 0 R/W 0 R/W 0 7 6 5 4 3 2 1 0 TCNT0H R/W 0 R/W 0 R/W 0 TCNT0H[7:0] R/W 0 R/W 0 When 16-bit mode is selected (the TCW0 bit is set to one) the Timer/Counter Register TCNT0H combined to the Timer/Counter Register TCNT0L gives direct access, both for read and write operations, to the Timer/Counter unit 16-bit counter. To ensure that both the high and low bytes are read and written simultaneously when the CPU accesses these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This temporary register is shared by all the other 16-bit registers. See "Accessing Registers in 16-bit Mode" on page 81 14.10.4 OCR0A - Timer/Counter0 Output Compare Register A Bit 0x13 (0x33) Read/Write Initial Value R/W 0 R/W 0 R/W 0 7 6 5 4 3 2 1 0 OCR0A R/W 0 R/W 0 R/W 0 OCR0A[7:0] R/W 0 R/W 0 The Output Compare Register A contains an 8-bit value that is continuously compared with the counter value (TCNT0L). A match can be used to generate an Output Compare interrupt. In 16-bit mode the OCR0A register contains the low byte of the 16-bit Output Compare Register. To ensure that both the high and the low bytes are written simultaneously when the CPU writes to these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This temporary register is shared by all the other 16-bit registers. See "Accessing Registers in 16-bit Mode" on page 81. 14.10.5 OCR0B - Timer/Counter0 Output Compare Register B Bit 0x12 (0x32) Read/Write Initial Value R/W 0 R/W 0 R/W 0 7 6 5 4 3 2 1 0 OCR0B R/W 0 R/W 0 R/W 0 OCR0B[7:0] R/W 0 R/W 0 The Output Compare Register B contains an 8-bit value that is continuously compared with the counter value (TCNT0L in 8-bit mode and TCNTH in 16-bit mode). A match can be used to generate an Output Compare interrupt. 86 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 In 16-bit mode the OCR0B register contains the high byte of the 16-bit Output Compare Register. To ensure that both the high and the low bytes are written simultaneously when the CPU writes to these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This temporary register is shared by all the other 16-bit registers. See "Accessing Registers in 16-bit Mode" on page 81. 14.10.6 TIMSK - Timer/Counter0 Interrupt Mask Register Bit 0x39 (0x59) Read/Write Initial Value 7 OCIE1D R/W 0 6 OCIE1A R/W 0 5 OCIE1B R/W 0 4 OCIE0A R/W 0 3 OCIE0B R/W 0 2 TOIE1 R/W 0 1 TOIE0 R/W 0 0 TICIE0 R 0 TIMSK * Bit 4 - OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable When the OCIE0A bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter0 Compare Match A interrupt is enabled. The corresponding interrupt is executed if a Compare Match in Timer/Counter0 occurs, i.e., when the OCF0A bit is set in the Timer/Counter 0 Interrupt Flag Register - TIFR0. * Bit 3 - OCIE0B: Timer/Counter Output Compare Match B Interrupt Enable When the OCIE0B bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter Compare Match B interrupt is enabled. The corresponding interrupt is executed if a Compare Match in Timer/Counter occurs, i.e., when the OCF0B bit is set in the Timer/Counter Interrupt Flag Register - TIFR0. * Bit 1 - TOIE0: Timer/Counter0 Overflow Interrupt Enable When the TOIE0 bit is written to one, and the I-bit in the Status Register is set, the Timer/Counter0 Overflow interrupt is enabled. The corresponding interrupt is executed if an overflow in Timer/Counter0 occurs, i.e., when the TOV0 bit is set in the Timer/Counter 0 Interrupt Flag Register - TIFR0. * Bit 0 - TICIE0: Timer/Counter0, Input Capture Interrupt Enable When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally enabled), the Timer/Counter1 Input Capture interrupt is enabled. The corresponding Interrupt Vector (See "Interrupts" on page 50.) is executed when the ICF0 flag, located in TIFR, is set. 87 7753C-AVR-07/09 14.10.7 TIFR - Timer/Counter0 Interrupt Flag Register Bit 0x38 (0x58) Read/Write Initial Value 7 OCF1D R/W 0 6 OCF1A R/W 0 5 OCF1B R/W 0 4 OCF0A R/W 0 3 OCF0B R/W 0 2 TOV1 R/W 0 1 TOV0 R/W 0 0 ICF0 R 0 TIFR * Bit 4- OCF0A: Output Compare Flag 0 A The OCF0A bit is set when a Compare Match occurs between the Timer/Counter0 and the data in OCR0A - Output Compare Register0. OCF0A is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF0A is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE0A (Timer/Counter0 Compare Match Interrupt Enable), and OCF0A are set, the Timer/Counter0 Compare Match Interrupt is executed. The OCF0A is also set in 16-bit mode when a Compare Match occurs between the Timer/Counter and 16-bit data in OCR0B/A. The OCF0A is not set in Input Capture mode when the Output Compare Register OCR0A is used as an Input Capture Register. * Bit 3 - OCF0B: Output Compare Flag 0 B The OCF0B bit is set when a Compare Match occurs between the Timer/Counter and the data in OCR0B - Output Compare Register0 B. OCF0B is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF0B is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE0B (Timer/Counter Compare B Match Interrupt Enable), and OCF0B are set, the Timer/Counter Compare Match Interrupt is executed. The OCF0B is not set in 16-bit Output Compare mode when the Output Compare Register OCR0B is used as the high byte of the 16-bit Output Compare Register or in 16-bit Input Capture mode when the Output Compare Register OCR0B is used as the high byte of the Input Capture Register. * Bit 1 - TOV0: Timer/Counter0 Overflow Flag The bit TOV0 is set when an overflow occurs in Timer/Counter0. TOV0 is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, TOV0 is cleared by writing a logic one to the flag. When the SREG I-bit, TOIE0 (Timer/Counter0 Overflow Interrupt Enable), and TOV0 are set, the Timer/Counter0 Overflow interrupt is executed. * Bits 0 - ICF0: Timer/Counter0, Input Capture Flag This flag is set when a capture event occurs on the ICP0 pin. When the Input Capture Register (ICR0) is set to be used as the TOP value, the ICF0 flag is set when the counter reaches the TOP value. ICF0 is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively, ICF0 can be cleared by writing a logic one to its bit location. 88 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 15. Timer/Counter1 Prescaler Figure 15-1 shows the Timer/Counter1 prescaler that supports two clocking modes, a synchronous clocking mode and an asynchronous clocking mode. The synchronous clocking mode uses the system clock (CK) as a clock timebase and asynchronous mode uses the fast peripheral clock (PCK) as a clock time base. The PCKE bit from the PLLCSR register enables the asynchronous mode when it is set (`1'). Figure 15-1. Timer/Counter1 Prescaler PCKE CK S PCK 64/32 MHz A PSR1 T1CK 14-BIT T/C PRESCALER T1CK/1024 T1CK/2048 T1CK/4096 T1CK/8192 T1CK/16384 T1CK/128 T1CK/256 0 CS10 CS11 CS12 CS13 TIMER/COUNTER1 COUNT ENABLE In the asynchronous clocking mode the clock selections are from PCK to PCK/16384 and stop, and in the synchronous clocking mode the clock selections are from CK to CK/16384 and stop. The clock options are described in Table 15-1 on page 91 and the Timer/Counter1 Control Register, TCCR1B. The frequency of the fast peripheral clock is 64 MHz or 32 MHz in Low Speed mode (the LSM bit in PLLCSR register is set to one). The Low Speed Mode is recommended to use when the supply voltage below 2.7 volts are used. 15.0.1 Prescaler Reset Setting the PSR1 bit in TCCR1B register resets the prescaler. It is possible to use the Prescaler Reset for synchronizing the Timer/Counter to program execution. Prescaler Initialization for Asynchronous Mode To change Timer/Counter1 to the asynchronous mode follow the procedure below: 1. Enable PLL. 2. Wait 100 s for PLL to stabilize. 3. Poll the PLOCK bit until it is set. 4. Set the PCKE bit in the PLLCSR register which enables the asynchronous mode. 15.0.2 T1CK/512 T1CK/16 T1CK/32 T1CK/64 T1CK/2 T1CK/4 T1CK/8 T1CK 89 7753C-AVR-07/09 15.1 15.1.1 Register Description PLLCSR - PLL Control and Status Register Bit 0x29 (0x49) Read/Write Initial value 7 LSM R/W 0 6 R 0 5 R 0 4 R 0 3 R 0 2 PCKE R/W 0 1 PLLE R/W 0/1 0 PLOCK R 0 PLLCSR * Bit 7- LSM: Low Speed Mode The Low Speed mode is set, if the LSM bit is written to one. Then the fast peripheral clock is scaled down to 32 MHz. The Low Speed Mode must be set, if the supply voltage is below 2.7 volts, because the Timer/Counter1 is not running fast enough on low voltage levels. It is recommended that the Timer/Counter1 is stopped whenever the LSM bit is changed. Note, that LSM can not be set if PLLCLK is used as a system clock. * Bit 6:3- Res: Reserved Bits These bits are reserved bits in the ATtiny261/461/861 and always read as zero. * Bit 2- PCKE: PCK Enable The PCKE bit change the Timer/Counter1 clock source. When it is set, the asynchronous clock mode is enabled and fast 64 MHz (or 32 MHz in Low Speed Mode) PCK clock is used as a Timer/Counter1 clock source. If this bit is cleared, the synchronous clock mode is enabled, and system clock CK is used as Timer/Counter1 clock source. It is safe to set this bit only when the PLL is locked i.e the PLOCK bit is 1. Note that the PCKE bit can be set only, if the PLL has been enabled earlier. The PLL is enabled when the CKSEL fuse has been programmed to 0x0001 (the PLL clock mode is selected) or the PLLE bit has been set to one. * Bit 1- PLLE: PLL Enable When the PLLE is set, the PLL is started and if needed internal RC-oscillator is started as a PLL reference clock. If PLL is selected as a system clock source the value for this bit is always 1. * Bit 0- PLOCK: PLL Lock Detector When the PLOCK bit is set, the PLL is locked to the reference clock. The PLOCK bit should be ignored during initial PLL lock-in sequence when PLL frequency overshoots and undershoots, before reaching steady state. The steady state is obtained within 100 s. After PLL lock-in it is recommended to check the PLOCK bit before enabling PCK for Timer/Counter1. 15.1.2 TCCR1B - Timer/Counter1 Control Register B Bit 0x2F (0x4F) Read/Write Initial value 7 R/W 0 6 PSR1 R/W 0 5 DTPS11 R/W 0 4 DTPS10 R/W 0 3 CS13 R/W 0 2 CS12 R/W 0 1 CS11 R/W 0 0 CS10 R/W 0 TCCR1B * Bit 7 - Res: Reserved Bit * Bit 6 - PSR1: Prescaler Reset Timer/Counter1 90 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 When this bit is set (one), the Timer/Counter prescaler (TCNT1 is unaffected) will be reset. The bit will be cleared by hardware after the operation is performed. Writing a zero to this bit will have no effect. This bit will always read as zero. * Bits 3:0 - CS13, CS12, CS11, CS10: Clock Select Bits 3, 2, 1, and 0 The Clock Select bits 3, 2, 1, and 0 define the prescaling source of Timer/Counter1. Table 15-1. CS13 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 Timer/Counter1 Prescale Select CS12 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 CS11 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 CS10 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Asynchronous Clocking Mode T/C1 stopped PCK PCK/2 PCK/4 PCK/8 PCK/16 PCK/32 PCK/64 PCK/128 PCK/256 PCK/512 PCK/1024 PCK/2048 PCK/4096 PCK/8192 PCK/16384 Synchronous Clocking Mode T/C1 stopped CK CK/2 CK/4 CK/8 CK/16 CK/32 CK/64 CK/128 CK/256 CK/512 CK/1024 CK/2048 CK/4096 CK/8192 CK/16384 The Stop condition provides a Timer Enable/Disable function. 91 7753C-AVR-07/09 16. Timer/Counter1 16.1 Features * * * * * * * * * 10/8-Bit Accuracy Three Independent Output Compare Units Clear Timer on Compare Match (Auto Reload) Glitch Free, Phase and Frequency Correct Pulse Width Modulator (PWM) Variable PWM Period Independent Dead Time Generators for each PWM channels Five Independent Interrupt Sources (TOV1, OCF1A, OCD1B, OCF1D, FPF1) High Speed Asynchronous and Synchronous Clocking Modes Separate Prescaler Unit 16.2 Overview Timer/Counter1 is a general purpose high speed Timer/Counter module, with three independent Output Compare Units, and with PWM support. The Timer/Counter1 features a high resolution and a high accuracy usage with the lower prescaling opportunities. It can also support three accurate and high speed Pulse Width Modulators using clock speeds up to 64 MHz. In PWM mode Timer/Counter1 and the output compare registers serve as triple stand-alone PWMs with non-overlapping non-inverted and inverted outputs. Similarly, the high prescaling opportunities make this unit useful for lower speed functions or exact timing functions with infrequent actions. A simplified block diagram of the Timer/Counter1 i s s h o w n i n F ig u r e 1 6 - 1 . F o r a ct u a l p la c e m e n t o f t h e I / O p i n s , r e f e r t o " P i n o u t ATtiny261/461/861" on page 2. The device-specific I/O register and bit locations are listed in the "Register Description" on page 115. 92 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 16-1. Timer/Counter1 Block Diagram TOV1 OCF1A OCF1B OCF1D OC1A OC1A OC1B OC1B OC1D OC1D FAULT_PROTECTION DEAD TIME GENERATOR OCW1A OCW1B OCW1D DEAD TIME GENERATOR DEAD TIME GENERATOR OCIE1B OCIE1D OCIE1A OCF1A OCF1D OCF1B TOIE1 FPIE1 T/C INT. MASK REGISTER (TIMSK) T/C INT. FLAG REGISTER (TIFR) TOV1 T/C CONTROL REGISTER A (TCCR1A) COM1A0 COM1B1 COM1B0 COM1A1 PWM1A PWM1B FOC1A FOC1B T/C CONTROL REGISTER B (TCCR1B) PSR1 PSR1 PSR1 CS13 CS12 CS11 CS10 T/C CONTROL REGISTER C (TCCR1C) COM1A1 COM1A0 COM1B1 COM1B0 COM1D1 COM1D0 FOC1D PWM1D T/C CONTROL REGISTER C (TCCR1D) FPNC1 FPEN1 FPES1 FPAC1 FPIE1 FPF1 WGM11 OC1OE0 WGM10 CLK TIMER/COUNTER1 (TCNT1) COUNT CLEAR DIRECTION TIMER/COUNTER1 CONTROL LOGIC OC1OE5 OC1OE4 OC1OE3 10-BIT COMPARATOR 10-BIT COMPARATOR 10-BIT COMPARATOR 10-BIT COMPARATOR T/C CONTROL REGISTER D (TCCR1E) 10-BIT OUTPUT COMPARE REGISTER A 10-BIT OUTPUT COMPARE REGISTER B 10-BIT OUTPUT COMPARE REGISTER C 10-BIT OUTPUT COMPARE REGISTER D 8-BIT OUTPUT COMPARE REGISTER A (OCR1A) 8-BIT OUTPUT COMPARE REGISTER B (OCR1B) 8-BIT OUTPUT COMPARE REGISTER C (OCR1C) 8-BIT OUTPUT COMPARE REGISTER D (OCR1D) 2-BIT HIGH BYTE REGISTER (TC1H) 8-BIT DATABUS 16.2.1 Speed The maximum speed of the Timer/Counter1 is 64 MHz. However, if a supply voltage below 2.7 volts is used, it is recommended to use the Low Speed Mode (LSM), because the Timer/Counter1 is not running fast enough on low voltage levels. In the Low Speed Mode the fast peripheral clock is scaled down to 32 MHz. For more details about the Low Speed Mode, see "PLLCSR - PLL Control and Status Register" on page 90. 16.2.2 Accuracy The Timer/Counter1 is a 10-bit Timer/Counter module that can alternatively be used as an 8-bit Timer/Counter. The Timer/Counter1 registers are basically 8-bit registers, but on top of that there is a 2-bit High Byte Register (TC1H) that can be used as a common temporary buffer to access the two MSBs of the 10-bit Timer/Counter1 registers by the AVR CPU via the 8-bit data bus, if the 10-bit accuracy is used. Whereas, if the two MSBs of the 10-bit registers are written to zero the Timer/Counter1 is working as an 8-bit Timer/Counter. When reading the low byte of any 8-bit register the two MSBs are written to the TC1H register, and when writing the low byte of any 8-bit register the two MSBs are written from the TC1H register. Special procedures must be followed when accessing the 10-bit Timer/Counter1 values via the 8-bit data bus. These procedures are described in the section "Accessing 10-Bit Registers" on page 112. OC1OE2 OC1OE1 FPF1 93 7753C-AVR-07/09 16.2.3 Registers The Timer/Counter (TCNT1) and Output Compare Registers (OCR1A, OCR1B, OCR1C and OCR1D) are 8-bit registers that are used as a data source to be compared with the TCNT1 contents. The OCR1A, OCR1B and OCR1D registers determine the action on the OC1A, OC1B and OC1D pins and they can also generate the compare match interrupts. The OCR1C holds the Timer/Counter TOP value, i.e. the clear on compare match value. The Timer/Counter1 High Byte Register (TC1H) is a 2-bit register that is used as a common temporary buffer to access the MSB bits of the Timer/Counter1 registers, if the 10-bit accuracy is used. Interrupt request (overflow TOV1, and compare matches OCF1A, OCF1B, OCF1D and fault protection FPF1) signals are visible in the Timer Interrupt Flag Register (TIFR) and Timer/Counter1 Control Register D (TCCR1D). The interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK) and the FPIE1 bit in the Timer/Counter1 Control Register D (TCCR1D). Control signals are found in the Timer/Counter Control Registers TCCR1A, TCCR1B, TCCR1C, TCCR1D and TCCR1E. 16.2.4 Synchronization In asynchronous clocking mode the Timer/Counter1 and the prescaler allow running the CPU from any clock source while the prescaler is operating on the fast peripheral clock (PCK) having frequency of 64 MHz (or 32 MHz in Low Speed Mode). This is possible because there is a synchronization boundary between the CPU clock domain and the fast peripheral clock domain. Figure 16-2 shows Timer/Counter 1 synchronization register block diagram and describes synchronization delays in between registers. Note that all clock gating details are not shown in the figure. The Timer/Counter1 register values go through the internal synchronization registers, which cause the input synchronization delay, before affecting the counter operation. The registers TCCR1A, TCCR1B, TCCR1C, TCCR1D, OCR1A, OCR1B, OCR1C and OCR1D can be read back right after writing the register. The read back values are delayed for the Timer/Counter1 (TCNT1) register, Timer/Counter1 High Byte Register (TC1H) and flags (OCF1A, OCF1B, OCF1D and TOV1), because of the input and output synchronization. The system clock frequency must be lower than half of the PCK frequency, because the synchronization mechanism of the asynchronous Timer/Counter1 needs at least two edges of the PCK when the system clock is high. If the frequency of the system clock is too high, it is a risk that data or control values are lost. 94 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 16-2. Timer/Counter1 Synchronization Register Block Diagram. 8-BIT DATABUS IO-registers OCR1A OCR1B OCR1C OCR1D TCCR1A TCCR1B TCCR1C TCCR1D TCNT1 TC1H OCF1A OCF1B OCF1D TOV1 Input synchronization registers OCR1A_SI TCNT1 Timer/Counter1 Output synchronization registers OCR1B_SI OCR1C_SI TCNT1_SO TC1H TC1H_SO OCR1D_SI TCCR1A_SI TCCR1B_SI OCF1A TCCR1C_SI TCCR1D_SI OCF1A_SO TCNT1 OCF1B TCNT1_SI TC1H_SI OCF1A_SI OCF1B_SO OCF1D OCF1D_SO OCF1B_SI OCF1D_SI TOV1 TOV1_SI TOV1_SO PCKE CK S A S PCK SYNC MODE ASYNC MODE A 1/2 CK Delay 1 CK Delay 1 CK Delay 1/2 CK Delay ~1/2 CK Delay 1 PCK Delay 1 PCK Delay ~1 CK Delay 16.2.5 Definitions Many register and bit references in this section are written in general form. A lower case "n" replaces the Timer/Counter number, in this case 0. A lower case "x" replaces the Output Compare Unit, in this case Compare Unit A, B, C or D. However, when using the register or bit defines in a program, the precise form must be used, i.e., TCNT1 for accessing Timer/Counter1 counter value and so on. The definitions in Table 16-1 are used extensively throughout the document. Table 16-1. BOTTOM MAX TOP Definitions The counter reaches the BOTTOM when it becomes 0. The counter reaches its MAXimum value when it becomes 0x3FF (decimal 1023). The counter reaches the TOP value (stored in the OCR1C) when it becomes equal to the highest value in the count sequence. The TOP has a value 0x0FF as default after reset. 95 7753C-AVR-07/09 16.3 Counter Unit The main part of the Timer/Counter1 is the programmable bi-directional counter unit. Figure 16-3 shows a block diagram of the counter and its surroundings. Figure 16-3. Counter Unit Block Diagram DATA BUS clkT1 count TCNT1 clear direction Control Logic TOV1 Timer/Counter1 Count Enable ( From Prescaler ) PCKE PCK CK bottom top Signal description (internal signals): count direction clear clkTn top bottom TCNT1 increment or decrement enable. Select between increment and decrement. Clear TCNT1 (set all bits to zero). Timer/Counter clock, referred to as clkT1 in the following. Signalize that TCNT1 has reached maximum value. Signalize that TCNT1 has reached minimum value (zero). Depending of the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkT1). The timer clock is generated from an synchronous system clock or an asynchronous PLL clock using the Clock Select bits (CS13:0) and the PCK Enable bit (PCKE). When no clock source is selected (CS13:0 = 0) the timer is stopped. However, the TCNT1 value can be accessed by the CPU, regardless of whether clkT1 is present or not. A CPU write overrides (has priority over) all counter clear or count operations. The counting sequence of the Timer/Counter1 is determined by the setting of the WGM10 and PWM1x bits located in the Timer/Counter1 Control Registers (TCCR1A, TCCR1C and TCCR1D). For more details about advanced counting sequences and waveform generation, see "Modes of Operation" on page 102. The Timer/Counter Overflow Flag (TOV1) is set according to the mode of operation selected by the PWM1x and WGM10 bits. The Overflow Flag can be used for generating a CPU interrupt. 16.3.1 Counter Initialization for Asynchronous Mode To change Timer/Counter1 to the asynchronous mode follow the procedure below: 1. Enable PLL. 2. Wait 100 s for PLL to stabilize. 3. Poll the PLOCK bit until it is set. 4. Set the PCKE bit in the PLLCSR register which enables the asynchronous mode. 96 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 16.4 Output Compare Unit The comparator continuously compares TCNT1 with the Output Compare Registers (OCR1A, OCR1B, OCR1C and OCR1D). Whenever TCNT1 equals to the Output Compare Register, the comparator signals a match. A match will set the Output Compare Flag (OCF1A, OCF1B or OCF1D) at the next timer clock cycle. If the corresponding interrupt is enabled, the Output Compare Flag generates an Output Compare interrupt. The Output Compare Flag is automatically cleared when the interrupt is executed. Alternatively, the flag can be cleared by software by writing a logical one to its I/O bit location. The Waveform Generator uses the match signal to generate an output according to operating mode set by the PWM1x, WGM10 and Compare Output mode (COM1x1:0) bits. The top and bottom signals are used by the Waveform Generator for handling the special cases of the extreme values in some modes of operation (See "Modes of Operation" on page 102.). Figure 16-4 shows a block diagram of the Output Compare unit. Figure 16-4. Output Compare Unit, Block Diagram 8-BIT DATA BUS OCRnx TCnH TCNTn 10-BIT OCRnx 10-BIT TCNTn = (10-bit Comparator ) OCFnx (Int.Req.) TOP BOTTOM FOCn PWMnx Waveform Generator WGM10 COMnX1:0 OCWnx The OCR1x Registers are double buffered when using any of the Pulse Width Modulation (PWM) modes. For the normal mode of operation, the double buffering is disabled. The double buffering synchronizes the update of the OCR1x Compare Registers to either top or bottom of the counting sequence. The synchronization prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free. See Figure 16-5 for an example. During the time between the write and the update operation, a read from OCR1A, OCR1B, OCR1C or OCR1D will read the contents of the temporary location. This means that the most recently written value always will read out of OCR1A, OCR1B, OCR1C or OCR1D. 97 7753C-AVR-07/09 Figure 16-5. Effects of Unsynchronized OCR Latching Compare Value changes Counter Value Compare Value Output Compare Waveform OCWnx Compare Value changes Counter Value Compare Value Output Compare Wafeform OCWnx Synchronized WFnx Latch Unsynchronized WFnx Latch Glitch 16.4.1 Force Output Compare In non-PWM waveform generation modes, the match output of the comparator can be forced by writing a one to the Force Output Compare (FOC1x) bit. Forcing Compare Match will not set the OCF1x Flag or reload/clear the timer, but the Waveform Output (OCW1x) will be updated as if a real Compare Match had occurred (the COM1x1:0 bits settings define whether the Waveform Output (OCW1x) is set, cleared or toggled). Compare Match Blocking by TCNT1 Write All CPU write operations to the TCNT1 Register will block any Compare Match that occur in the next timer clock cycle, even when the timer is stopped. This feature allows OCR1x to be initialized to the same value as TCNT1 without triggering an interrupt when the Timer/Counter clock is enabled. Using the Output Compare Unit Since writing TCNT1 in any mode of operation will block all Compare Matches for one timer clock cycle, there are risks involved when changing TCNT1 when using the Output Compare Unit, independently of whether the Timer/Counter is running or not. If the value written to TCNT1 equals the OCR1x value, the Compare Match will be missed, resulting in incorrect waveform generation. Similarly, do not write the TCNT1 value equal to BOTTOM when the counter is down-counting. The setup of the Waveform Output (OCW1x) should be performed before setting the Data Direction Register for the port pin to output. The easiest way of setting the OCW1x value is to use the Force Output Compare (FOC1x) strobe bits in Normal mode. The OC1x keeps its value even when changing between Waveform Generation modes. Be aware that the COM1x1:0 bits are not double buffered together with the compare value. Changing the COM1x1:0 bits will take effect immediately. 16.4.2 16.4.3 98 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 16.5 Dead Time Generator The Dead Time Generator is provided for the Timer/Counter1 PWM output pairs to allow driving external power control switches safely. The Dead Time Generator is a separate block that can be used to insert dead times (non-overlapping times) for the Timer/Counter1 complementary output pairs OC1x and OC1x when the PWM mode is enabled and the COM1x1:0 bits are set to "01". The sharing of tasks is as follows: the Waveform Generator generates the Waveform Output (OCW1x) and the Dead Time Generator generates the non-overlapping PWM output pair from the Waveform Output. Three Dead Time Generators are provided, one for each PWM output. The non-overlap time is adjustable and the PWM output and it's complementary output are adjusted separately, and independently for both PWM outputs. Figure 16-6. Output Compare Unit, Block Diagram top bottom FOCn OCnx OCnx pin OCnx pin Waveform Generator OCWnx Dead Time Generator OCnx PWMnx WGM10 COMnx CK OR PCK CLOCK DTPSn DTnH DTnL The Dead Time Generation is based on the 4-bit down counters that count the dead time, as shown in Figure 16-7. There is a dedicated prescaler in front of the Dead Time Generator that can divide the Timer/Counter1 clock (PCK or CK) by 1, 2, 4 or 8. This provides for large range of dead times that can be generated. The prescaler is controlled by two control bits DTPS11..10. The block has also a rising and falling edge detector that is used to start the dead time counting period. Depending on the edge, one of the transitions on the rising edges, OC1x or OC1x is delayed until the counter has counted to zero. The comparator is used to compare the counter with zero and stop the dead time insertion when zero has been reached. The counter is loaded with a 4-bit DT1H or DT1L value from DT1 I/O register, depending on the edge of the Waveform Output (OCW1x) when the dead time insertion is started. The Output Compare Output are delayed by one timer clock cycle at minimum from the Waveform Output when the Dead Time is adjusted to zero. The outputs OC1x and OC1x are inverted, if the PWM Inversion Mode bit PWM1X is set. This will also cause both outputs to be high during the dead time. Figure 16-7. Dead Time Generator PWM1X COMPARATOR OCnx CK OR PCK CLOCK DEAD TIME PRE-SCALER CLOCK CONTROL 4-BIT COUNTER OCnx DTPSn DTnH DTnL PWM1X TCCRnB REGISTER OCWnx DTn I/O REGISTER DATA BUS (8-bit) 99 7753C-AVR-07/09 The length of the counting period is user adjustable by selecting the dead time prescaler setting by using the DTPS11:10 control bits, and selecting then the dead time value in I/O register DT1. The DT1 register consists of two 4-bit fields, DT1H and DT1L that control the dead time periods of the PWM output and its' complementary output separately in terms of the number of prescaled dead time generator clock cycles. Thus the rising edge of OC1x and OC1x can have different dead time periods as the tnon-overlap / rising edge is adjusted by the 4-bit DT1H value and the tnon-overlap / falling edge is adjusted by the 4-bit DT1L value. Figure 16-8. The Complementary Output Pair, COM1x1:0 = 1 OCWnx OCnx OCnx (COMnx = 1) t non-overlap / rising edge t non-overlap / falling edge 16.6 Compare Match Output Unit The Compare Output Mode (COM1x1:0) bits have two functions. The Waveform Generator uses the COM1x1:0 bits for defining the inverted or non-inverted Waveform Output (OCW1x) at the next Compare Match. Also, the COM1x1:0 bits control the OC1x and OC1x pin output source. Figure 16-9 shows a simplified schematic of the logic affected by the COM1x1:0 bit setting. The I/O Registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the general I/O Port Control Registers (DDR and PORT) that are affected by the COM1x1:0 bits are shown. In Normal Mode (non-PWM) the Dead Time Generator is disabled and it is working like a synchronizer: the Output Compare (OC1x) is delayed from the Waveform Output (OCW1x) by one timer clock cycle. Whereas in Fast PWM Mode and in Phase and Frequency Correct PWM Mode when the COM1x1:0 bits are set to "01" both the non-inverted and the inverted Output Compare output are generated, and an user programmable Dead Time delay is inserted for these complementary output pairs (OC1x and OC1x). The functionality in PWM modes is similar to Normal mode when any other COM1x1:0 bit setup is used. When referring to the OC1x state, the reference is for the Output Compare output (OC1x) from the Dead Time Generator, not the OC1x pin. If a system reset occur, the OC1x is reset to "0". The general I/O port function is overridden by the Output Compare (OC1x / OC1x) from the Dead Time Generator if either of the COM1x1:0 bits are set. However, the OC1x pin direction (input or output) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction Register bit for the OC1x and OC1x pins (DDR_OC1x and DDR_OC1x) must be set as output before the OC1x and OC1x values are visible on the pin. The port override function is independent of the Output Compare mode. 100 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 The design of the Output Compare Pin Configuration logic allows initialization of the OC1x state before the output is enabled. Note that some COM1x1:0 bit settings are reserved for certain modes of operation. For Output Compare Pin Configurations refer to Table 16-2 on page 103, Table 16-3 on page 105, Table 16-4 on page 107, and Table 16-5 on page 109. Figure 16-9. Compare Match Output Unit, Schematic clk I/O WGM11 OC1OE1:0 COM1A1:0 Output Compare Pin Configuration DQ PORTB0 0 1 0 DQ DDRB0 1 OC1A PIN DQ PORTB1 OCW1A clk Tn Dead Time Q Generator A Q OC1A OC1A 1 0 OC1A PIN DQ DDRB1 WGM11 OC1OE3:2 COM1B1:0 Output Compare Pin Configuration DQ PORTB2 DATA BUS DQ DDRB2 OCW1B clk Tn OC1B OC1B 2 1 0 1 0 OC1B PIN DQ PORTB3 Dead Time Q Generator B Q 1 0 1 0 OC1B PIN DQ DDRB3 WGM11 OC1OE5:4 COM1D1:0 Output Compare Pin Configuration DQ PORTB4 2 1 0 1 0 OC1D PIN DQ DDRB4 OCW1D clk Tn OC1D OC1D DQ PORTB5 Dead Time Q Generator D Q 1 0 1 0 OC1D PIN DQ DDRB5 101 7753C-AVR-07/09 16.6.1 Compare Output Mode and Waveform Generation The Waveform Generator uses the COM1x1:0 bits differently in Normal mode and PWM modes. For all modes, setting the COM1x1:0 = 0 tells the Waveform Generator that no action on the OCW1x Output is to be performed on the next Compare Match. For compare output actions in the non-PWM modes refer to Table 16-6 on page 115. For fast PWM mode, refer to Table 16-7 on page 115, and for the Phase and Frequency Correct PWM refer to Table 16-8 on page 116. A change of the COM1x1:0 bits state will have effect at the first Compare Match after the bits are written. For non-PWM modes, the action can be forced to have immediate effect by using the FOC1x strobe bits. 16.7 Modes of Operation The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is defined by the combination of the Waveform Generation mode (bits PWM1x and WGM10) and Compare Output mode (COM1x1:0) bits. The Compare Output mode bits do not affect the counting sequence, while the Waveform Generation mode bits do. The COM1x1:0 bits control whether the PWM output generated should be inverted, non-inverted or complementary. For non-PWM modes the COM1x1:0 bits control whether the output should be set, cleared, or toggled at a Compare Match. 16.7.1 Normal Mode The simplest mode of operation is the Normal mode (PWM1x = 0), the counter counts from BOTTOM to TOP (defined as OCR1C) then restarts from BOTTOM. The OCR1C defines the TOP value for the counter, hence also its resolution, and allows control of the Compare Match output frequency. In toggle Compare Output Mode the Waveform Output (OCW1x) is toggled at Compare Match between TCNT1 and OCR1x. In non-inverting Compare Output Mode the Waveform Output is cleared on the Compare Match. In inverting Compare Output Mode the Waveform Output is set on Compare Match. The timing diagram for the Normal mode is shown in Figure 16-10. The counter value (TCNT1) that is shown as a histogram in the timing diagram is incremented until the counter value matches the TOP value. The counter is then cleared at the following clock cycle The diagram includes the Waveform Output (OCW1x) in toggle Compare Mode. The small horizontal line marks on the TCNT1 slopes represent Compare Matches between OCR1x and TCNT1. Figure 16-10. Normal Mode, Timing Diagram TOVn Interrupt Flag Set OCnx Interrupt Flag Set TCNTn OCWnx (COMnx=1) Period 1 2 3 4 102 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 The Timer/Counter Overflow Flag (TOV1) is set in the same clock cycle as the TCNT1 becomes zero. The TOV1 Flag in this case behaves like a 11th bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt, that automatically clears the TOV1 Flag, the timer resolution can be increased by software. There are no special cases to consider in the Normal mode, a new counter value can be written anytime. The Output Compare Unit can be used to generate interrupts at some given time. Using the Output Compare to generate waveforms in Normal mode is not recommended, since this will occupy too much of the CPU time. For generating a waveform, the OCW1x output can be set to toggle its logical level on each Compare Match by setting the Compare Output mode bits to toggle mode (COM1x1:0 = 1). The OC1x value will not be visible on the port pin unless the data direction for the pin is set to output. The waveform generated will have a maximum frequency of fOC1x = fclkT1/4 when OCR1C is set to zero. The waveform frequency is defined by the following equation: f clkT1 f OC1x = --------------------------------------------2 ( 1 + OCR1C ) Resolution shows how many bit is required to express the value in the OCR1C register. It is calculated by following equation: ResolutionPWM = log2(OCR1C + 1). The Output Compare Pin configurations in Normal Mode are described in Table 16-2. Table 16-2. COM1x1 0 0 1 1 Output Compare Pin Configurations in Normal Mode COM1x0 0 1 0 1 OC1x Pin Disconnected Disconnected Disconnected Disconnected OC1x Pin Disconnected OC1x OC1x OC1x 16.7.2 Fast PWM Mode The fast Pulse Width Modulation or fast PWM mode (PWM1x = 1 and WGM10 = 0) provides a high frequency PWM waveform generation option. The fast PWM differs from the other PWM option by its single-slope operation. The counter counts from BOTTOM to TOP (defined as OCR1C) then restarts from BOTTOM. In non-inverting Compare Output mode the Waveform Output (OCW1x) is cleared on the Compare Match between TCNT1 and OCR1x and set at BOTTOM. In inverting Compare Output mode, the Waveform Output is set on Compare Match and cleared at BOTTOM. In complementary Compare Output mode the Waveform Output is cleared on the Compare Match and set at BOTTOM. Due to the single-slope operation, the operating frequency of the fast PWM mode can be twice as high as the Phase and Frequency Correct PWM mode that use dual-slope operation. This high frequency makes the fast PWM mode well suited for power regulation, rectification, and DAC applications. High frequency allows physically small sized external components (coils, capacitors), and therefore reduces total system cost. The timing diagram for the fast PWM mode is shown in Figure 16-11. The counter is incremented until the counter value matches the TOP value. The counter is then cleared at the following timer clock cycle. The TCNT1 value is in the timing diagram shown as a histogram for illustrating the single-slope operation. 103 7753C-AVR-07/09 The diagram includes the Waveform Output in non-inverted and inverted Compare Output modes. The small horizontal line marks on the TCNT1 slopes represent Compare Matches between OCR1x and TCNT1. Figure 16-11. Fast PWM Mode, Timing Diagram OCRnx Interrupt Flag Set OCRnx Update and TOVn Interrupt Flag Set TCNTn OCWnx (COMnx1:0 = 2) OCWnx (COMnx1:0 = 3) Period 1 2 3 4 5 6 7 The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches TOP. If the interrupt is enabled, the interrupt handler routine can be used for updating the compare value. In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC1x pins. Setting the COM1x1:0 bits to two will produce a non-inverted PWM and setting the COM1x1:0 to three will produce an inverted PWM output. Setting the COM1x1:0 bits to one will enable complementary Compare Output mode and produce both the non-inverted (OC1x) and inverted output (OC1x). The actual value will only be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by setting (or clearing) the Waveform Output (OCW1x) at the Compare Match between OCR1x and TCNT1, and clearing (or setting) the Waveform Output at the timer clock cycle the counter is cleared (changes from TOP to BOTTOM). The PWM frequency for the output can be calculated by the following equation: f clkT1 f OCnxPWM = -----------N The N variable represents the number of steps in single-slope operation. The value of N equals either to the TOP value. The extreme values for the OCR1C Register represents special cases when generating a PWM waveform output in the fast PWM mode. If the OCR1C is set equal to BOTTOM, the output will be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR1C equal to MAX will result in a constantly high or low output (depending on the polarity of the output set by the COM1x1:0 bits.) A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting the Waveform Output (OCW1x) to toggle its logical level on each Compare Match (COM1x1:0 = 1). The waveform generated will have a maximum frequency of fOC1 = fclkT1/4 when OCR1C is set to three. 104 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 The general I/O port function is overridden by the Output Compare value (OC1x / OC1x) from the Dead Time Generator, if either of the COM1x1:0 bits are set and the Data Direction Register bits for the OC1X and OC1X pins are set as an output. If the COM1x1:0 bits are cleared, the actual value from the port register will be visible on the port pin. The Output Compare Pin configurations are described in Table 16-3. Table 16-3. COM1x1 0 0 1 1 Output Compare Pin Configurations in Fast PWM Mode COM1x0 0 1 0 1 OC1x Pin Disconnected OC1x Disconnected Disconnected OC1x Pin Disconnected OC1x OC1x OC1x 16.7.3 Phase and Frequency Correct PWM Mode The Phase and Frequency Correct PWM Mode (PWMx = 1 and WGM10 = 1) provides a high resolution Phase and Frequency Correct PWM waveform generation option. The Phase and Frequency Correct PWM mode is based on a dual-slope operation. The counter counts repeatedly from BOTTOM to TOP (defined as OCR1C) and then from TOP to BOTTOM. In non-inverting Compare Output Mode the Waveform Output (OCW1x) is cleared on the Compare Match between TCNT1 and OCR1x while upcounting, and set on the Compare Match while down-counting. In inverting Output Compare mode, the operation is inverted. In complementary Compare Output Mode, the Waveform Output is cleared on the Compare Match and set at BOTTOM. The dual-slope operation has lower maximum operation frequency than single slope operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control applications. The timing diagram for the Phase and Frequency Correct PWM mode is shown on Figure 16-12 in which the TCNT1 value is shown as a histogram for illustrating the dual-slope operation. The counter is incremented until the counter value matches TOP. When the counter reaches TOP, it changes the count direction. The TCNT1 value will be equal to TOP for one timer clock cycle. The diagram includes the Waveform Output (OCW1x) in non-inverted and inverted Compare Output Mode. The small horizontal line marks on the TCNT1 slopes represent Compare Matches between OCR1x and TCNT1. 105 7753C-AVR-07/09 Figure 16-12. Phase and Frequency Correct PWM Mode, Timing Diagram OCnx Interrupt Flag Set OCRnx Update TOVn Interrupt Flag Set TCNTn OCWnx (COMnx = 2) OCWnx (COMnx = 3) Period 1 2 3 The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches BOTTOM. The Interrupt Flag can be used to generate an interrupt each time the counter reaches the BOTTOM value. In the Phase and Frequency Correct PWM mode, the compare unit allows generation of PWM waveforms on the OC1x pins. Setting the COM1x1:0 bits to two will produce a non-inverted PWM and setting the COM1x1:0 to three will produce an inverted PWM output. Setting the COM1A1:0 bits to one will enable complementary Compare Output mode and produce both the non-inverted (OC1x) and inverted output (OC1x). The actual values will only be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by clearing (or setting) the Waveform Output (OCW1x) at the Compare Match between OCR1x and TCNT1 when the counter increments, and setting (or clearing) the Waveform Output at Compare Match when the counter decrements. The PWM frequency for the output when using the Phase and Frequency Correct PWM can be calculated by the following equation: f clkT1 f OCnxPCPWM = -----------N The N variable represents the number of steps in dual-slope operation. The value of N equals to the TOP value. The extreme values for the OCR1C Register represent special cases when generating a PWM waveform output in the Phase and Frequency Correct PWM mode. If the OCR1C is set equal to BOTTOM, the output will be continuously low and if set equal to MAX the output will be continuously high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic values. The general I/O port function is overridden by the Output Compare value (OC1x / OC1x) from the Dead Time Generator, if either of the COM1x1:0 bits are set and the Data Direction Register bits for the OC1X and OC1X pins are set as an output. If the COM1x1:0 bits are cleared, the actual value from the port register will be visible on the port pin. The configurations of the Output Compare Pins are described in Table 16-4. 106 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 16-4. COM1x1 0 0 1 1 Output Compare pin configurations in Phase and Frequency Correct PWM Mode COM1x0 0 1 0 1 OC1x Pin Disconnected OC1x Disconnected Disconnected OC1x Pin Disconnected OC1x OC1x OC1x 16.7.4 PWM6 Mode The PWM6 Mode (PWM1A = 1, WGM11 = 1 and WGM10 = x) provide PWM waveform generation option e.g. for controlling Brushless DC (BLDC) motors. In the PWM6 Mode the OCR1A Register controls all six Output Compare waveforms as the same Waveform Output (OCW1A) from the Waveform Generator is used for generating all waveforms. The PWM6 Mode also provides an Output Compare Override Enable Register (OC1OE) that can be used with an instant response for disabling or enabling the Output Compare pins. If the Output Compare Override Enable bit is cleared, the actual value from the port register will be visible on the port pin. The PWM6 Mode provides two counter operation modes, a single-slope operation and a dual-slope operation. If the single-slope operation is selected (the WGM10 bit is set to 0), the counter counts from BOTTOM to TOP (defined as OCR1C) then restart from BOTTOM like in Fast PWM Mode. The PWM waveform is generated by setting (or clearing) the Waveform Output (OCW1A) at the Compare Match between OCR1A and TCNT1, and clearing (or setting) the Waveform Output at the timer clock cycle the counter is cleared (changes from TOP to BOTTOM). The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches the TOP and, if the interrupt is enabled, the interrupt handler routine can be used for updating the compare value. Whereas, if the dual-slope operation is selected (the WGM10 bit is set to 1), the counter counts repeatedly from BOTTOM to TOP (defined as OCR1C) and then from TOP to BOTTOM like in Phase and Frequency Correct PWM Mode. The PWM waveform is generated by setting (or clearing) the Waveform Output (OCW1A) at the Compare Match between OCR1A and TCNT1 when the counter increments, and clearing (or setting) the Waveform Output at the he Compare Match between OCR1A and TCNT1 when the counter decrements. The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches the BOTTOM and, if the interrupt is enabled, the interrupt handler routine can be used for updating the compare value. The timing diagram for the PWM6 Mode in single-slope operation (WGM11 = 0) when the COM1A1:0 bits are set to "10" is shown in Figure 16-13. The counter is incremented until the counter value matches the TOP value. The counter is then cleared at the following timer clock cycle. The TCNT1 value is in the timing diagram shown as a histogram for illustrating the single-slope operation. The timing diagram includes Output Compare pins OC1A and OC1A, and the corresponding Output Compare Override Enable bits (OC1OE1..OC1OE0). 107 7753C-AVR-07/09 Figure 16-13. PWM6 Mode, Single-slope Operation, Timing Diagram TCNT1 OCW1A OC1OE0 OC1A Pin OC1OE1 OC1A Pin OC1OE2 OC1B Pin OC1OE3 OC1B Pin OC1OE4 OC1D Pin OC1OE5 OC1D Pin The general I/O port function is overridden by the Output Compare value (OC1x / OC1x) from the Dead Time Generator if either of the COM1x1:0 bits are set. The Output Compare pins can also be overridden by the Output Compare Override Enable bits OC1OE5..OC1OE0. If an Override Enable bit is cleared, the actual value from the port register will be visible on the port pin and, if the Override Enable bit is set, the Output Compare pin is allowed to be connected on the port pin. The Output Compare Pin configurations are described in Table 16-5. 108 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 16-5. COM1A1 0 0 1 1 COM1B1 0 0 1 1 COM1D1 0 0 1 1 Output Compare Pin configurations in PWM6 Mode COM1A0 0 1 0 1 COM1B0 0 1 0 1 COM1D0 0 1 0 1 OC1A Pin (PB0) Disconnected OC1A * OC1OE0 OC1A * OC1OE0 OC1A * OC1OE0 OC1B Pin (PB2) Disconnected OC1A * OC1OE2 OC1A * OC1OE2 OC1A * OC1OE2 OC1D Pin (PB4) Disconnected OC1A * OC1OE4 OC1A * OC1OE4 OC1A * OC1OE4 OC1A Pin (PB1) Disconnected OC1A * OC1OE1 OC1A * OC1OE1 OC1A * OC1OE1 OC1B Pin (PB3) Disconnected OC1A * OC1OE3 OC1A * OC1OE3 OC1A * OC1OE3 OC1D Pin (PB5) Disconnected OC1A * OC1OE5 OC1A * OC1OE5 OC1A * OC1OE5 16.8 Timer/Counter Timing Diagrams The Timer/Counter is a synchronous design and the timer clock (clkT1) is therefore shown as a clock enable signal in the following figures. The figures include information on when Interrupt Flags are set. Figure 16-14 contains timing data for basic Timer/Counter operation. The figure shows the count sequence close to the MAX value in all modes other than Phase and Frequency Correct PWM Mode. Figure 16-15 shows the same timing data, but with the prescaler enabled, in all modes other than Phase and Frequency Correct PWM Mode. Figure 16-16 shows the setting of OCF1A, OCF1B and OCF1D in all modes, and Figure 16-17 shows the setting of TOV1 in Phase and Frequency Correct PWM Mode. Figure 16-14. Timer/Counter Timing Diagram, no Prescaling clkPCK clkTn (clkPCK /1) TCNTn TOP - 1 TOP BOTTOM BOTTOM + 1 TOVn 109 7753C-AVR-07/09 Figure 16-15. Timer/Counter Timing Diagram, with Prescaler (fclkT1/8) clkPCK clkTn (clkPCK /8) TCNTn TOP - 1 TOP BOTTOM BOTTOM + 1 TOVn Figure 16-16. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (fclkT1/8) clkPCK clkTn (clkPCK /8) TCNTn OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2 OCRnx OCRnx Value OCFnx Figure 16-17. Timer/Counter Timing Diagram, with Prescaler (fclkT1/8) clkPCK clkTn (clkPCK /8) TCNTn BOTTOM + 1 BOTTOM + 1 BOTTOM BOTTOM + 1 TOVn 110 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 16.9 Fault Protection Unit The Timer/Counter1 incorporates a Fault Protection unit that can disable the PWM output pins, if an external event is triggered. The external signal indicating an event can be applied via the external interrupt INT0 pin or alternatively, via the analog-comparator unit. The Fault Protection unit is illustrated by the block diagram shown in Figure 16-18. The elements of the block diagram that are not directly a part of the Fault Protection unit are gray shaded. Figure 16-18. Fault Protection Unit Block Diagram FAULT_PROTECTION (Int. Req.) ACO* Analog Comparator INT0 FPAC1 FPNC1 FPES1 FPEN1 Noise Canceler Edge Detector Timer/Counter1 When the Fault Protection mode is enabled by the Fault Protection Enable (FPEN1) bit and a change of the logic level (an event) occurs on the external interrupt pin (INT0), alternatively on the Analog Comparator output (ACO), and this change confirms to the setting of the edge detector, a Fault Protection mode will be triggered. When a Fault Protection is triggered, the COM1x bits are cleared, Output Comparators are disconnected from the PWM output pins and the PORTB register bits are connected on the PWM output pins. The Fault Protection Enable (FPEN1) is automatically cleared at the same system clock as the COM1nx bits are cleared. If the Fault Protection Interrupt Enable bit (FPIE1) is set, a Fault Protection interrupt is generated and the FPEN1 bit is cleared. Alternatively the FPEN1 bit can be polled by software to figure out when the Timer/Counter has entered to Fault Protection mode. 16.9.1 Fault Protection Trigger Source The main trigger source for the Fault Protection unit is the external interrupt pin (INT0). Alternatively the Analog Comparator output can be used as trigger source for the Fault Protection unit. The Analog Comparator is selected as trigger source by setting the Fault Protection Analog Comparator (FPAC1) bit in the Timer/Counter1 Control Register (TCCR1D). Be aware that changing trigger source can trigger a Fault Protection mode. Therefore it is recommended to clear the FPF1 flag after changing trigger source, setting edge detector or enabling the Fault Protection. Both the external interrupt pin (INT0) and the Analog Comparator output (ACO) inputs are sampled using the same technique as for the T0 pin (Figure 13-1 on page 70). The edge detector is also identical. However, when the noise canceler is enabled, additional logic is inserted before the edge detector, which increases the delay by four system clock cycles. An Input Capture can also be triggered by software by controlling the port of the INT0 pin. 16.9.2 Noise Canceler The noise canceler improves noise immunity by using a simple digital filtering scheme. The noise canceler input is monitored over four samples, and all four must be equal for changing the output that in turn is used by the edge detector. The noise canceler is enabled by setting the Fault Protection Noise Canceler (FPNC1) bit in Timer/Counter1 Control Register D (TCCR1D). When enabled the noise canceler introduces additional four system clock cycles of delay from a change applied to the input. The noise canceler uses the system clock and is therefore not affected by the prescaler. 111 7753C-AVR-07/09 16.10 Accessing 10-Bit Registers If 10-bit values are written to the TCNT1 and OCR1A/B/C/D registers, the 10-bit registers can be byte accessed by the AVR CPU via the 8-bit data bus using two read or write operations. The 10-bit registers have a common 2-bit Timer/Counter1 High Byte Register (TC1H) that is used for temporary storing of the two MSBs of the 10-bit access. The same TC1H register is shared between all 10-bit registers. Accessing the low byte triggers the 10-bit read or write operation. When the low byte of a 10-bit register is written by the CPU, the high byte stored in the TC1H register, and the low byte written are both copied into the 10-bit register in the same clock cycle. When the low byte of a 10-bit register is read by the CPU, the high byte of the 10-bit register is copied into the TC1H register in the same clock cycle as the low byte is read. To do a 10-bit write, the high byte must be written to the TC1H register before the low byte is written. For a 10-bit read, the low byte must be read before the high byte. The following code examples show how to access the 10-bit timer registers assuming that no interrupts updates the TC1H register. The same principle can be used directly for accessing the OCR1A/B/C/D registers. Assembly Code Example ... ; Set TCNT1 to 0x01FF ldi r17,0x01 ldi r16,0xFF out TC1H,r17 out TCNT1,r16 ; Read TCNT1 into r17:r16 in r16,TCNT1 in r17,TC1H ... C Code Example unsigned int i; ... /* Set TCNT1 to 0x01FF */ TC1H = 0x01; TCNT1 = 0xFF; /* Read TCNT1 into i */ i = TCNT1; i |= ((unsigned int)TC1H << 8); ... Note: 1. The example code assumes that the part specific header file is included. For I/O registers located in extended I/O map, "IN", "OUT", "SBIS", "SBIC", "CBI", and "SBI" instructions must be replaced with instructions that allow access to extended I/O. Typically "LDS" and "STS" combined with "SBRS", "SBRC", "SBR", and "CBR". The assembly code example returns the TCNT1 value in the r17:r16 register pair. 112 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 It is important to notice that accessing 10-bit registers are atomic operations. If an interrupt occurs between the two instructions accessing the 10-bit register, and the interrupt code updates the TC1H register by accessing the same or any other of the 10-bit timer registers, then the result of the access outside the interrupt will be corrupted. Therefore, when both the main code and the interrupt code update the TC1H register, the main code must disable the interrupts during the 16-bit access. The following code examples show how to do an atomic read of the TCNT1 register contents. Reading any of the OCR1A/B/C/D registers can be done by using the same principle. Assembly Code Example TIM1_ReadTCNT1: ; Save global interrupt flag in r18,SREG ; Disable interrupts cli ; Read TCNT1 into r17:r16 in r16,TCNT1 in r17,TC1H ; Restore global interrupt flag out SREG,r18 ret C Code Example unsigned int TIM1_ReadTCNT1( void ) { unsigned char sreg; unsigned int i; /* Save global interrupt flag */ sreg = SREG; /* Disable interrupts */ _CLI(); /* Read TCNT1 into i */ i = TCNT1; i |= ((unsigned int)TC1H << 8); /* Restore global interrupt flag SREG = sreg; return i; } Note: 1. The example code assumes that the part specific header file is included. For I/O registers located in extended I/O map, "IN", "OUT", "SBIS", "SBIC", "CBI", and "SBI" instructions must be replaced with instructions that allow access to extended I/O. Typically "LDS" and "STS" combined with "SBRS", "SBRC", "SBR", and "CBR". The assembly code example returns the TCNT1 value in the r17:r16 register pair. 113 7753C-AVR-07/09 The following code examples show how to do an atomic write of the TCNT1 register contents. Writing any of the OCR1A/B/C/D registers can be done by using the same principle. Assembly Code Example TIM1_WriteTCNT1: ; Save global interrupt flag in r18,SREG ; Disable interrupts cli ; Set TCNT1 to r17:r16 out TC1H,r17 out TCNT1,r16 ; Restore global interrupt flag out SREG,r18 ret C Code Example void TIM1_WriteTCNT1( unsigned int i ) { unsigned char sreg; unsigned int i; /* Save global interrupt flag */ sreg = SREG; /* Disable interrupts */ _CLI(); /* Set TCNT1 to i */ TC1H = (i >> 8); TCNT1 = (unsigned char)i; /* Restore global interrupt flag */ SREG = sreg; } Note: 1. The example code assumes that the part specific header file is included. For I/O registers located in extended I/O map, "IN", "OUT", "SBIS", "SBIC", "CBI", and "SBI" instructions must be replaced with instructions that allow access to extended I/O. Typically "LDS" and "STS" combined with "SBRS", "SBRC", "SBR", and "CBR". The assembly code example requires that the r17:r16 register pair contains the value to be written to TCNT1. 16.10.1 Reusing the temporary high byte register If writing to more than one 10-bit register where the high byte is the same for all registers written, then the high byte only needs to be written once. However, note that the same rule of atomic operation described previously also applies in this case. 114 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 16.11 Register Description 16.11.1 TCCR1A - Timer/Counter1 Control Register A Bit 0x30 (0x50) Read/Write Initial value 7 COM1A1 6 COM1A0 5 COM1B1 4 COM1B0 3 FOC1A 2 FOC1B 1 PWM1A 0 PWM1B TCCR1A R/W 0 R/W 0 R/W 0 R/W 0 W 0 W 0 R/W 0 R/W 0 * Bits 7,6 - COM1A1, COM1A0: Comparator A Output Mode, Bits 1 and 0 These bits control the behavior of the Waveform Output (OCW1A) and the connection of the Output Compare pin (OC1A). If one or both of the COM1A1:0 bits are set, the OC1A output overrides the normal port functionality of the I/O pin it is connected to. The complementary OC1B output is connected only in PWM modes when the COM1A1:0 bits are set to "01". Note that the Data Direction Register (DDR) bit corresponding to the OC1A and OC1A pins must be set in order to enable the output driver. The function of the COM1A1:0 bits depends on the PWM1A, WGM10 and WGM11 bit settings. Table 16-6 shows the COM1A1:0 bit functionality when the PWM1A bit is set to Normal Mode (non-PWM). Table 16-6. COM1A1..0 00 01 10 11 Compare Output Mode, Normal Mode (non-PWM) OCW1A Behavior Normal port operation. Toggle on Compare Match. Clear on Compare Match. Set on Compare Match. OC1A Pin Disconnected Connected Connected Connected OC1A Pin Disconnected Disconnected Disconnected Disconnected Table 16-7 shows the COM1A1:0 bit functionality when the PWM1A, WGM10 and WGM11 bits are set to fast PWM mode. Table 16-7. COM1A1..0 00 01 10 11 Compare Output Mode, Fast PWM Mode OCW1A Behavior Normal port operation. Cleared on Compare Match. Set when TCNT1 = 0x000. Cleared on Compare Match. Set when TCNT1 = 0x000. Set on Compare Match. Cleared when TCNT1 = 0x000. OC1A Disconnected Connected Connected Connected OC1A Disconnected Connected Disconnected Disconnected 115 7753C-AVR-07/09 Table 16-8 shows the COM1A1:0 bit functionality when the PWM1A, WGM10 and WGM11 bits are set to Phase and Frequency Correct PWM Mode. Table 16-8. COM1A1..0 00 01 10 11 Compare Output Mode, Phase and Frequency Correct PWM Mode OCW1A Behavior Normal port operation. Cleared on Compare Match when up-counting. Set on Compare Match when down-counting. Cleared on Compare Match when up-counting. Set on Compare Match when down-counting. Set on Compare Match when up-counting. Cleared on Compare Match when down-counting. OC1A Pin Disconnected Connected Connected Connected OC1A Pin Disconnected Connected Disconnected Disconnected Table 16-9 shows the COM1A1:0 bit functionality when the PWM1A, WGM10 and WGM11 bits are set to single-slope PWM6 Mode. In the PWM6 Mode the same Waveform Output (OCW1A) is used for generating all waveforms and the Output Compare values OC1A and OC1A are connected on the all OC1x and OC1x pins as described below. Table 16-9. COM1A1..0 00 01 10 11 Compare Output Mode, Single-Slope PWM6 Mode OCW1A Behavior Normal port operation. Cleared on Compare Match. Set when TCNT1 = 0x000. Cleared on Compare Match. Set when TCNT1 = 0x000. Set on Compare Match. Cleared when TCNT1 = 0x000. OC1x Pin Disconnected OC1A OC1A OC1A OC1x Pin Disconnected OC1A OC1A OC1A Table 16-10 shows the COM1A1:0 bit functionality when the PWM1A, WGM10 and WGM11 bits are set to dual-slope PWM6 Mode.I Table 16-10. Compare Output Mode, Dual-Slope PWM6 Mode COM1A1..0 00 01 10 11 OCW1A Behavior Normal port operation. Cleared on Compare Match when up-counting. Set on Compare Match when down-counting. Cleared on Compare Match when up-counting. Set on Compare Match when down-counting. Set on Compare Match when up-counting. Cleared on Compare Match when down-counting. OC1x Pin Disconnected OC1A OC1A OC1A OC1x Pin Disconnected OC1A OC1A OC1A * Bits 5,4 - COM1B1, COM1B0: Comparator B Output Mode, Bits 1 and 0 These bits control the Behavior of the Waveform Output (OCW1B) and the connection of the Output Compare pin (OC1B). If one or both of the COM1B1:0 bits are set, the OC1B output overrides the normal port functionality of the I/O pin it is connected to. The complementary OC1B output is connected only in PWM modes when the COM1B1:0 bits are set to "01". 116 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Note that the Data Direction Register (DDR) bit corresponding to the OC1B pin must be set in order to enable the output driver. The function of the COM1B1:0 bits depends on the PWM1B and WGM10 bit settings. Table 16-11 shows the COM1B1:0 bit functionality when the PWM1B bit is set to Normal Mode (non-PWM). Table 16-11. Compare Output Mode, Normal Mode (non-PWM) COM1B1..0 00 01 10 11 OCW1B Behavior Normal port operation. Toggle on Compare Match. Clear on Compare Match. Set on Compare Match. OC1B Pin Disconnected Connected Connected Connected OC1B Pin Disconnected Disconnected Disconnected Disconnected Table 16-12 shows the COM1B1:0 bit functionality when the PWM1B and WGM10 bits are set to Fast PWM Mode. Table 16-12. Compare Output Mode, Fast PWM Mode COM1B1..0 00 01 10 11 OCW1B Behavior Normal port operation. Cleared on Compare Match. Set when TCNT1 = 0x000. Cleared on Compare Match. Set when TCNT1 = 0x000. Set on Compare Match. Cleared when TCNT1 = 0x000. OC1B Pin Disconnected Connected Connected Connected OC1B Pin Disconnected Connected Disconnected Disconnected Table 16-13 shows the COM1B1:0 bit functionality when the PWM1B and WGM10 bits are set to Phase and Frequency Correct PWM Mode. Table 16-13. Compare Output Mode, Phase and Frequency Correct PWM Mode COM1B1..0 00 01 10 11 OCW1B Behavior Normal port operation. Cleared on Compare Match when up-counting. Set on Compare Match when down-counting. Cleared on Compare Match when up-counting. Set on Compare Match when down-counting. Set on Compare Match when up-counting. Cleared on Compare Match when down-counting. OC1B Pin Disconnected Connected Connected Connected OC1B Pin Disconnected Connected Disconnected Disconnected * Bit 3 - FOC1A: Force Output Compare Match 1A The FOC1A bit is only active when the PWM1A bit specify a non-PWM mode. Writing a logical one to this bit forces a change in the Waveform Output (OCW1A) and the Output Compare pin (OC1A) according to the values already set in COM1A1 and COM1A0. If COM1A1 and COM1A0 written in the same cycle as FOC1A, the new settings will be used. The Force Output Compare bit can be used to change the output pin value regardless of the timer value. 117 7753C-AVR-07/09 The automatic action programmed in COM1A1 and COM1A0 takes place as if a compare match had occurred, but no interrupt is generated. The FOC1A bit is always read as zero. * Bit 2 - FOC1B: Force Output Compare Match 1B The FOC1B bit is only active when the PWM1B bit specify a non-PWM mode. Writing a logical one to this bit forces a change in the Waveform Output (OCW1B) and the Output Compare pin (OC1B) according to the values already set in COM1B1 and COM1B0. If COM1B1 and COM1B0 written in the same cycle as FOC1B, the new settings will be used. The Force Output Compare bit can be used to change the output pin value regardless of the timer value. The automatic action programmed in COM1B1 and COM1B0 takes place as if a compare match had occurred, but no interrupt is generated. The FOC1B bit is always read as zero. * Bit 1 - PWM1A: Pulse Width Modulator A Enable When set (one) this bit enables PWM mode based on comparator OCR1A * Bit 0 - PWM1B: Pulse Width Modulator B Enable When set (one) this bit enables PWM mode based on comparator OCR1B. 16.11.2 TCCR1B - Timer/Counter1 Control Register B Bit 0x2F (0x4F) Read/Write Initial value 7 PWM1X R/W 0 6 PSR1 R/W 0 5 DTPS11 R/W 0 4 DTPS10 R/W 0 3 CS13 R/W 0 2 CS12 R/W 0 1 CS11 R/W 0 0 CS10 R/W 0 TCCR1B * Bit 7 - PWM1X: PWM Inversion Mode When this bit is set (one), the PWM Inversion Mode is selected and the Dead Time Generator outputs, OC1x and OC1x are inverted. * Bit 6 - PSR1: Prescaler Reset Timer/Counter1 When this bit is set (one), the Timer/Counter1 prescaler (TCNT1 is unaffected) will be reset. The bit will be cleared by hardware after the operation is performed. Writing a zero to this bit will have no effect. This bit will always read as zero. * Bits 5,4 - DTPS11, DTPS10: Dead Time Prescaler Bits The Timer/Counter1 Control Register B is a 8-bit read/write register. The dedicated Dead Time prescaler in front of the Dead Time Generator can divide the Timer/Counter1 clock (PCK or CK) by 1, 2, 4 or 8 providing a large range of dead times that can be generated. The Dead Time prescaler is controlled by two bits DTPS11 and DTPS10 from the Dead Time Prescaler register. These bits define the division factor of the Dead Time prescaler. The division factors are given in Table 16-14. 118 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 16-14. Division factors of the Dead Time prescaler DTPS11 0 0 1 1 DTPS10 0 1 0 1 Prescaler divides the T/C1 clock by 1x (no division) 2x 4x 8x * Bits 3.. 0 - CS13, CS12, CS11, CS10: Clock Select Bits 3, 2, 1, and 0 The Clock Select bits 3, 2, 1, and 0 define the prescaling source of Timer/Counter1. Table 16-15. Timer/Counter1 Prescaler Select CS13 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 CS12 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 CS11 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 CS10 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Asynchronous Clocking Mode T/C1 stopped PCK PCK/2 PCK/4 PCK/8 PCK/16 PCK/32 PCK/64 PCK/128 PCK/256 PCK/512 PCK/1024 PCK/2048 PCK/4096 PCK/8192 PCK/16384 Synchronous Clocking Mode T/C1 stopped CK CK/2 CK/4 CK/8 CK/16 CK/32 CK/64 CK/128 CK/256 CK/512 CK/1024 CK/2048 CK/4096 CK/8192 CK/16384 The Stop condition provides a Timer Enable/Disable function. 16.11.3 TCCR1C - Timer/Counter1 Control Register C Bit 0x27 (0x47) Read/Write Initial value 7 R/W 0 6 R/W 0 5 R/W 0 4 R/W 0 3 COM1D1 R/W 0 2 COM1D0 R/W 0 1 FOC1D R/W 0 0 PWM1D R/W 0 TCCR1C COM1A1S COM1A0S COM1B1S COM1B0S * Bits 7,6 - COM1A1S, COM1A0S: Comparator A Output Mode, Bits 1 and 0 These bits are the shadow bits of the COM1A1 and COM1A0 bits that are described in the section "TCCR1A - Timer/Counter1 Control Register A" on page 115. 119 7753C-AVR-07/09 * Bits 5,4 - COM1B1S, COM1B0S: Comparator B Output Mode, Bits 1 and 0 These bits are the shadow bits of the COM1A1 and COM1A0 bits that are described in the section "TCCR1A - Timer/Counter1 Control Register A" on page 115. * Bits 3,2 - COM1D1, COM1D0: Comparator D Output Mode, Bits 1 and 0 These bits control the Behavior of the Waveform Output (OCW1D) and the connection of the Output Compare pin (OC1D). If one or both of the COM1D1:0 bits are set, the OC1D output overrides the normal port functionality of the I/O pin it is connected to. The complementary OC1D output is connected only in PWM modes when the COM1D1:0 bits are set to "01". Note that the Data Direction Register (DDR) bit corresponding to the OC1D pin must be set in order to enable the output driver. The function of the COM1D1:0 bits depends on the PWM1D and WGM10 bit settings. Table 16-16 shows the COM1D1:0 bit functionality when the PWM1D bit is set to a Normal Mode (non-PWM). Table 16-16. Compare Output Mode, Normal Mode (non-PWM) COM1D1..0 00 01 10 11 OCW1D Behavior Normal port operation. Toggle on Compare Match. Clear on Compare Match. Set on Compare Match. OC1D Pin Disconnected Connected Connected Connected OC1D Pin Disconnected Disconnected Disconnected Disconnected Table 16-17 shows the COM1D1:0 bit functionality when the PWM1D and WGM10 bits are set to Fast PWM Mode. Table 16-17. Compare Output Mode, Fast PWM Mode COM1D1..0 00 01 10 11 OCW1D Behavior Normal port operation. Cleared on Compare Match. Set when TCNT1 = 0x000. Cleared on Compare Match. Set when TCNT1 = 0x000. Set on Compare Match. Clear when TCNT1 = 0x000. OC1D Pin Disconnected Connected Connected Connected OC1D Pin Disconnected Connected Disconnected Disconnected Table 16-18 on page 121 shows the COM1D1:0 bit functionality when the PWM1D and WGM10 bits are set to Phase and Frequency Correct PWM Mode. 120 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 16-18. Compare Output Mode, Phase and Frequency Correct PWM Mode COM1D1..0 00 01 10 11 OCW1D Behavior Normal port operation. Cleared on Compare Match when up-counting. Set on Compare Match when down-counting. Cleared on Compare Match when up-counting. Set on Compare Match when down-counting. Set on Compare Match when up-counting. Cleared on Compare Match when down-counting. OC1D Pin Disconnected Connected Connected Connected OC1D Pin Disconnected Connected Disconnected Disconnected * Bit 1 - FOC1D: Force Output Compare Match 1D The FOC1D bit is only active when the PWM1D bit specify a non-PWM mode. Writing a logical one to this bit forces a change in the Waveform Output (OCW1D) and the Output Compare pin (OC1D) according to the values already set in COM1D1 and COM1D0. If COM1D1 and COM1D0 written in the same cycle as FOC1D, the new settings will be used. The Force Output Compare bit can be used to change the output pin value regardless of the timer value. The automatic action programmed in COM1D1 and COM1D0 takes place as if a compare match had occurred, but no interrupt is generated. The FOC1D bit is always read as zero. * Bit 0 - PWM1D: Pulse Width Modulator D Enable When set (one) this bit enables PWM mode based on comparator OCR1D. 16.11.4 TCCR1D - Timer/Counter1 Control Register D Bit 0x26 (0x46) Read/Write Initial value 7 FPIE1 R/W 0 6 FPEN1 R/W 0 5 FPNC1 R/W 0 4 FPES1 R/W 0 3 FPAC1 R/W 0 2 FPF1 R/W 0 1 WGM11 R/W 0 0 WGM10 R/W 0 TCCR1D * Bit 7 - FPIE1: Fault Protection Interrupt Enable Setting this bit (to one) enables the Fault Protection Interrupt. * Bit 6- FPEN1: Fault Protection Mode Enable Setting this bit (to one) activates the Fault Protection Mode. * Bit 5 - FPNC1: Fault Protection Noise Canceler Setting this bit activates the Fault Protection Noise Canceler. When the noise canceler is activated, the input from the Fault Protection Pin (INT0) is filtered. The filter function requires four successive equal valued samples of the INT0 pin for changing its output. The Fault Protection is therefore delayed by four Oscillator cycles when the noise canceler is enabled. * Bit 4 - FPES1: Fault Protection Edge Select This bit selects which edge on the Fault Protection pin (INT0) is used to trigger a fault event. When the FPES1 bit is written to zero, a falling (negative) edge is used as trigger, and when the FPES1 bit is written to one, a rising (positive) edge will trigger the fault. 121 7753C-AVR-07/09 * Bit 3 - FPAC1: Fault Protection Analog Comparator Enable When written logic one, this bit enables the Fault Protection function in Timer/Counter1 to be triggered by the Analog Comparator. The comparator output is in this case directly connected to the Fault Protection front-end logic, making the comparator utilize the noise canceler and edge select features of the Timer/Counter1 Fault Protection interrupt. When written logic zero, no connection between the Analog Comparator and the Fault Protection function exists. To make the comparator trigger the Timer/Counter1 Fault Protection interrupt, the FPIE1 bit in the Timer/Counter1 Control Register D (TCCR1D) must be set. * Bit 2- FPF1: Fault Protection Interrupt Flag When the FPIE1 bit is set (one), the Fault Protection Interrupt is enabled. Activity on the pin will cause an interrupt request even, if the Fault Protection pin is configured as an output. The corresponding interrupt of Fault Protection Interrupt Request is executed from the Fault Protection Interrupt Vector. The bit FPF1 is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, FPF1 is cleared after a synchronization clock cycle by writing a logical one to the flag. When the SREG I-bit, FPIE1 and FPF1 are set, the Fault Interrupt is executed. * Bits 1:0 - WGM11, WGM10: Waveform Generation Mode Bits This bit associated with the PWMx bits control the counting sequence of the counter, the source for type of waveform generation to be used, see Table 16-19. Modes of operation supported by the Timer/Counter1 are: Normal mode (counter), Fast PWM Mode, Phase and Frequency Correct PWM and PWM6 Modes. Table 16-19. Waveform Generation Mode Bit Description PWM1x 0 1 1 1 1 WGM11..10 Timer/Counter Mode of Operation xx 00 01 10 11 Normal Fast PWM Phase and Frequency Correct PWM PWM6 / Single-slope PWM6 / Dual-slope TOP OCR1C OCR1C OCR1C OCR1C OCR1C Update of OCR1x at Immediate TOP BOTTOM TOP BOTTOM TOV1 Flag Set on TOP TOP BOTTOM TOP BOTTOM 16.11.5 TCCR1E - Timer/Counter1 Control Register E Bit 0x00 (0x20) Read/Write Initial value 7 R 0 6 R 0 5 OC1OE5 R/W 0 4 OC1OE4 R/W 0 3 OC1OE3 R/W 0 2 OC1OE2 R/W 0 1 OC1OE1 R/W 0 0 OC1OE0 R/W 0 TCCR1E * Bits 7:6 - Res: Reserved Bits These bits are reserved bits in the ATtiny261/461/861 and always reads as zero. * Bits 5:0 - OC1OE5:OC1OE0: Output Compare Override Enable Bits These bits are the Output Compare Override Enable bits that are used to connect or disconnect the Output Compare Pins in PWM6 Modes with an instant response on the corresponding Output Compare Pins. 122 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 The actual value from the port register will be visible on the port pin, when the Output Compare Override Enable Bit is cleared. Table 16-20 shows the Output Compare Override Enable Bits and their corresponding Output Compare pins. Table 16-20. Output Compare Override Enable Bits vs. Output Compare Pins OC1OE0 OC1A (PB0) OC1OE1 OC1A (PB1) OC1OE2 OC1B (PB2) OC1OE3 OC1B (PB3) OC1OE4 OC1D (PB4) OC1OE5 OC1D (PB5) 16.11.6 TCNT1 - Timer/Counter1 Bit 0x2E (0x4E) Read/Write Initial value 7 MSB R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 6 5 4 3 2 1 0 LSB R/W 0 TCNT1 This 8-bit register contains the value of Timer/Counter1. The Timer/Counter1 is realized as a 10-bit up/down counter with read and write access. Due to synchronization of the CPU, Timer/Counter1 data written into Timer/Counter1 is delayed by one and half CPU clock cycles in synchronous mode and at most one CPU clock cycles for asynchronous mode. When a 10-bit accuracy is preferred, special procedures must be followed for accessing the 10-bit TCNT1 register via the 8-bit AVR data bus. These procedures are described in section "Accessing 10-Bit Registers" on page 112. Alternatively the Timer/Counter1 can be used as an 8-bit Timer/Counter. Note that the Timer/Counter1 always starts counting up after writing the TCNT1 register. 16.11.7 TC1H - Timer/Counter1 High Byte Bit 0x25 (0x45) Read/Write Initial value 7 R 0 6 R 0 5 R 0 4 R 0 3 R 0 2 R 0 1 TC19 R/W 0 0 TC18 R/W 0 TC1H The temporary Timer/Counter1 register is an 2-bit read/write register. * Bits 7:2 - Res: Reserved Bits These bits are reserved bits in the ATtiny261/461/861 and always reads as zero. * Bits 1:0 - TC19, TC18: Two MSB bits of the 10-bit accesses If 10-bit accuracy is used, the Timer/Counter1 High Byte Register (TC1H) is used for temporary storing the MSB bits (TC19, TC18) of the 10-bit accesses. The same TC1H register is shared between all 10-bit registers within the Timer/Counter1. Note that special procedures must be followed when accessing the 10-bit TCNT1 register via the 8-bit AVR data bus. These procedures are described in section "Accessing 10-Bit Registers" on page 112. 123 7753C-AVR-07/09 16.11.8 OCR1A - Timer/Counter1 Output Compare Register A Bit 0x2D (0x4D) Read/Write Initial value 7 MSB R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 6 5 4 3 2 1 0 LSB R/W 0 OCR1A The output compare register A is an 8-bit read/write register. The Timer/Counter Output Compare Register A contains data to be continuously compared with Timer/Counter1. Actions on compare matches are specified in TCCR1A. A compare match does only occur if Timer/Counter1 counts to the OCR1A value. A software write that sets TCNT1 and OCR1A to the same value does not generate a compare match. A compare match will set the compare interrupt flag OCF1A after a synchronization delay following the compare event. Note that, if 10-bit accuracy is used special procedures must be followed when accessing the internal 10-bit Output Compare Registers via the 8-bit AVR data bus. These procedures are described in section "Accessing 10-Bit Registers" on page 112. 16.11.9 OCR1B - Timer/Counter1 Output Compare Register B Bit 0x2C (0x4C) Read/Write Initial value 7 MSB R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 6 5 4 3 2 1 0 LSB R/W 0 OCR1B The output compare register B is an 8-bit read/write register. The Timer/Counter Output Compare Register B contains data to be continuously compared with Timer/Counter1. Actions on compare matches are specified in TCCR1. A compare match does only occur if Timer/Counter1 counts to the OCR1B value. A software write that sets TCNT1 and OCR1B to the same value does not generate a compare match. A compare match will set the compare interrupt flag OCF1B after a synchronization delay following the compare event. Note that, if 10-bit accuracy is used special procedures must be followed when accessing the internal 10-bit Output Compare Registers via the 8-bit AVR data bus. These procedures are described in section "Accessing 10-Bit Registers" on page 112. 16.11.10 OCR1C - Timer/Counter1 Output Compare Register C Bit 0x2B (0x4B) Read/Write Initial value 7 MSB R/W 1 R/W 1 R/W 1 R/W 1 R/W 1 R/W 1 R/W 1 6 5 4 3 2 1 0 LSB R/W 1 OCR1C The output compare register C is an 8-bit read/write register. The Timer/Counter Output Compare Register C contains data to be continuously compared with Timer/Counter1, and a compare match will clear TCNT1. This register has the same function in Normal mode and PWM modes. 124 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Note that, if a smaller value than three is written to the Output Compare Register C, the value is automatically replaced by three as it is a minimum value allowed to be written to this register. Note that, if 10-bit accuracy is used special procedures must be followed when accessing the internal 10-bit Output Compare Registers via the 8-bit AVR data bus. These procedures are described in section "Accessing 10-Bit Registers" on page 112. 16.11.11 OCR1D - Timer/Counter1 Output Compare Register D Bit 0x2A (0x4A) Read/Write Initial value 7 MSB R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 6 5 4 3 2 1 0 LSB R/W 0 OCR1D The output compare register D is an 8-bit read/write register. The Timer/Counter Output Compare Register D contains data to be continuously compared with Timer/Counter1. Actions on compare matches are specified in TCCR1A. A compare match does only occur if Timer/Counter1 counts to the OCR1D value. A software write that sets TCNT1 and OCR1D to the same value does not generate a compare match. A compare match will set the compare interrupt flag OCF1D after a synchronization delay following the compare event. Note that, if 10-bit accuracy is used special procedures must be followed when accessing the internal 10-bit Output Compare Registers via the 8-bit AVR data bus. These procedures are described in section "Accessing 10-Bit Registers" on page 112. 16.11.12 TIMSK - Timer/Counter1 Interrupt Mask Register Bit 0x39 (0x59) Read/Write Initial value 7 OCIE1D R/W 0 6 OCIE1A R/W 0 5 OCIE1B R/W 0 4 OCIE0A R/W 0 3 OCIE0B R/W 0 2 TOIE1 R/W 0 1 TOIE0 R/W 0 0 TICIE0 R/W 0 TIMSK * Bit 7- OCIE1D: Timer/Counter1 Output Compare Interrupt Enable When the OCIE1D bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter1 Compare MatchD, interrupt is enabled. The corresponding interrupt at vector $010 is executed if a compare matchD occurs. The Compare Flag in Timer/Counter1 is set (one) in the Timer/Counter Interrupt Flag Register. * Bit 6 - OCIE1A: Timer/Counter1 Output Compare Interrupt Enable When the OCIE1A bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter1 Compare MatchA, interrupt is enabled. The corresponding interrupt at vector $003 is executed if a compare matchA occurs. The Compare Flag in Timer/Counter1 is set (one) in the Timer/Counter Interrupt Flag Register. * Bit 5 - OCIE1B: Timer/Counter1 Output Compare Interrupt Enable When the OCIE1B bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter1 Compare MatchB, interrupt is enabled. The corresponding interrupt at vector $009 is executed if a compare matchB occurs. The Compare Flag in Timer/Counter1 is set (one) in the Timer/Counter Interrupt Flag Register. 125 7753C-AVR-07/09 * Bit 2 - TOIE1: Timer/Counter1 Overflow Interrupt Enable When the TOIE1 bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter1 Overflow interrupt is enabled. The corresponding interrupt (at vector $004) is executed if an overflow in Timer/Counter1 occurs. The Overflow Flag (Timer1) is set (one) in the Timer/Counter Interrupt Flag Register - TIFR. 16.11.13 TIFR - Timer/Counter1 Interrupt Flag Register Bit 0x38 (0x58) Read/Write Initial value 7 OCF1D R/W 0 6 OCF1A R/W 0 5 OCF1B R/W 0 4 OCF0A R/W 0 3 OCF0B R/W 0 2 TOV1 R/W 0 1 TOV0 R/W 0 0 ICF0 R/W 0 TIFR * Bit 7- OCF1D: Output Compare Flag 1D The OCF1D bit is set (one) when compare match occurs between Timer/Counter1 and the data value in OCR1D - Output Compare Register 1D. OCF1D is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF1D is cleared, after synchronization clock cycle, by writing a logic one to the flag. When the I-bit in SREG, OCIE1D, and OCF1D are set (one), the Timer/Counter1 D compare match interrupt is executed. * Bit 6 - OCF1A: Output Compare Flag 1A The OCF1A bit is set (one) when compare match occurs between Timer/Counter1 and the data value in OCR1A - Output Compare Register 1A. OCF1A is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF1A is cleared, after synchronization clock cycle, by writing a logic one to the flag. When the I-bit in SREG, OCIE1A, and OCF1A are set (one), the Timer/Counter1 A compare match interrupt is executed. * Bit 5 - OCF1B: Output Compare Flag 1B The OCF1B bit is set (one) when compare match occurs between Timer/Counter1 and the data value in OCR1B - Output Compare Register 1A. OCF1B is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF1B is cleared, after synchronization clock cycle, by writing a logic one to the flag. When the I-bit in SREG, OCIE1B, and OCF1B are set (one), the Timer/Counter1 B compare match interrupt is executed. * Bit 2 - TOV1: Timer/Counter1 Overflow Flag In Normal Mode and Fast PWM Mode the TOV1 bit is set (one) each time the counter reaches TOP at the same clock cycle when the counter is reset to BOTTOM. In Phase and Frequency Correct PWM Mode the TOV1 bit is set (one) each time the counter reaches BOTTOM at the same clock cycle when zero is clocked to the counter. The bit TOV1 is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, TOV1 is cleared, after synchronization clock cycle, by writing a logical one to the flag. When the SREG I-bit, and TOIE1 (Timer/Counter1 Overflow Interrupt Enable), and TOV1 are set (one), the Timer/Counter1 Overflow interrupt is executed. 126 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 16.11.14 DT1 - Timer/Counter1 Dead Time Value Bit 0x24 (0x44) Read/Write Initial value 7 DT1H3 R/W 0 6 DT1H2 R/W 0 5 DT1H1 R/W 0 4 DT1H0 R/W 0 3 DT1L3 R/W 0 2 DT1L2 R/W 0 1 DT1L1 R/W 0 0 DT1L0 R/W 0 DT1 The dead time value register is an 8-bit read/write register. The dead time delay of all Timer/Counter1 channels are adjusted by the dead time value register, DT1. The register consists of two fields, DT1H3..0 and DT1L3..0, one for each complementary output. Therefore a different dead time delay can be adjusted for the rising edge of OC1x and the rising edge of OC1x. * Bits 7:4- DT1H3:DT1H0: Dead Time Value for OC1x Output The dead time value for the OC1x output. The dead time delay is set as a number of the prescaled timer/counter clocks. The minimum dead time is zero and the maximum dead time is the prescaled time/counter clock period multiplied by 15. * Bits 3:0- DT1L3:DT1L0: Dead Time Value for OC1x Output The dead time value for the OC1x output. The dead time delay is set as a number of the prescaled timer/counter clocks. The minimum dead time is zero and the maximum dead time is the prescaled time/counter clock period multiplied by 15. 127 7753C-AVR-07/09 17. USI - Universal Serial Interface 17.1 Features * * * * * * Two-wire Synchronous Data Transfer (Master or Slave) Three-wire Synchronous Data Transfer (Master or Slave) Data Received Interrupt Wakeup from Idle Mode In Two-wire Mode: Wake-up from All Sleep Modes, Including Power-down Mode Two-wire Start Condition Detector with Interrupt Capability 17.2 Overview The Universal Serial Interface, or USI, provides the basic hardware resources needed for serial communication. Combined with a minimum of control software, the USI allows significantly higher transfer rates and uses less code space than solutions based on software only. Interrupts are included to minimize the processor load. A simplified block diagram of the USI is shown on Figure 17-1. For the actual placement of I/O pins, refer to "Pinout ATtiny261/461/861" on page 2. CPU accessible I/O Registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed in the "Register Descriptions" on page 135. Figure 17-1. Universal Serial Interface, Block Diagram DQ LE Bit7 Bit0 DO (Output only) DI/SDA 3 2 1 0 TIM0 COMP (Input/Open Drain) USIDR USIDB 3 2 1 0 [1] 0 1 CLOCK HOLD DATA BUS USIOIF USISIF USIDC USIPF 4-bit Counter USCK/SCL (Input/Open Drain) USISR 2 Two-wire Clock Control Unit USIWM1 USIWM0 USICS1 USICS0 USICLK USIOIE USISIE USICR The 8-bit USI Data Register is directly accessible via the data bus and contains the incoming and outgoing data. The register has no buffering so the data must be read as quickly as possible to ensure that no data is lost. The USI Data Register is a serial shift register and the most significant bit that is the output of the serial shift register is connected to one of two output pins depending of the wire mode configuration. A transparent latch is inserted between the USI Data Register Output and output pin, which delays the change of data output to the opposite clock edge of the data input sampling. The serial input is always sampled from the Data Input (DI) pin independent of the configuration. 128 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 USITC ATtiny261/ATtiny461/ATtiny861 The 4-bit counter can be both read and written via the data bus, and can generate an overflow interrupt. Both the USI Data Register and the counter are clocked simultaneously by the same clock source. This allows the counter to count the number of bits received or transmitted and generate an interrupt when the transfer is complete. Note that when an external clock source is selected the counter counts both clock edges. In this case the counter counts the number of edges, and not the number of bits. The clock can be selected from three different sources: The USCK pin, Timer/Counter0 Compare Match or from software. The Two-wire clock control unit can generate an interrupt when a start condition is detected on the Two-wire bus. It can also generate wait states by holding the clock pin low after a start condition is detected, or after the counter overflows. 17.3 17.3.1 Functional Descriptions Three-wire Mode The USI Three-wire mode is compliant to the Serial Peripheral Interface (SPI) mode 0 and 1, but does not have the slave select (SS) pin functionality. However, this feature can be implemented in software if necessary. Pin names used by this mode are: DI, DO, and USCK. Figure 17-2. Three-wire Mode Operation, Simplified Diagram DO Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 DI USCK SLAVE DO Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 DI USCK PORTxn MASTER Figure 17-2 shows two USI units operating in Three-wire mode, one as Master and one as Slave. The two USI Data Register are interconnected in such way that after eight USCK clocks, the data in each register are interchanged. The same clock also increments the USI's 4-bit counter. The Counter Overflow (interrupt) Flag, or USIOIF, can therefore be used to determine when a transfer is completed. The clock is generated by the Master device software by toggling the USCK pin via the PORT Register or by writing a one to the USITC bit in USICR. 129 7753C-AVR-07/09 Figure 17-3. Three-wire Mode, Timing Diagram CYCLE USCK USCK DO DI MSB MSB 6 6 5 5 4 4 3 3 2 2 1 1 LSB LSB ( Reference ) 1 2 3 4 5 6 7 8 A B C D E The Three-wire mode timing is shown in Figure 17-3. At the top of the figure is a USCK cycle reference. One bit is shifted into the USI Data Register (USIDR) for each of these cycles. The USCK timing is shown for both external clock modes. In External Clock mode 0 (USICS0 = 0), DI is sampled at positive edges, and DO is changed (Data Register is shifted by one) at negative edges. External Clock mode 1 (USICS0 = 1) uses the opposite edges versus mode 0, i.e., samples data at negative and changes the output at positive edges. The USI clock modes corresponds to the SPI data mode 0 and 1. Referring to the timing diagram (Figure 17-3.), a bus transfer involves the following steps: 1. The Slave device and Master device sets up its data output and, depending on the protocol used, enables its output driver (mark A and B). The output is set up by writing the data to be transmitted to the USI Data Register. Enabling of the output is done by setting the corresponding bit in the port Data Direction Register. Note that point A and B does not have any specific order, but both must be at least one half USCK cycle before point C where the data is sampled. This must be done to ensure that the data setup requirement is satisfied. The 4-bit counter is reset to zero. 2. The Master generates a clock pulse by software toggling the USCK line twice (C and D). The bit value on the slave and master's data input (DI) pin is sampled by the USI on the first edge (C), and the data output is changed on the opposite edge (D). The 4-bit counter will count both edges. 3. Step 2. is repeated eight times for a complete register (byte) transfer. 4. After eight clock pulses (i.e., 16 clock edges) the counter will overflow and indicate that the transfer is completed. The data bytes transferred must now be processed before a new transfer can be initiated. The overflow interrupt will wake up the processor if it is set to Idle mode. Depending of the protocol used the slave device can now set its output to high impedance. 17.3.2 SPI Master Operation Example The following code demonstrates how to use the USI module as a SPI Master: SPITransfer: sts ldi sts ldi sts lds sbrs USIDR,r16 r16,(1< 130 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 rjmp lds ret SPITransfer_loop r16,USIDR The code is size optimized using only eight instructions (+ ret). The code example assumes that the DO and USCK pins are enabled as output in the DDRA or DDRB Register. The value stored in register r16 prior to the function is called is transferred to the Slave device, and when the transfer is completed the data received from the Slave is stored back into the r16 Register. The second and third instructions clears the USI Counter Overflow Flag and the USI counter value. The fourth and fifth instruction set Three-wire mode, positive edge Shift Register clock, count at USITC strobe, and toggle USCK. The loop is repeated 16 times. The following code demonstrates how to use the USI module as a SPI Master with maximum speed (fsck = fck/4): SPITransfer_Fast: sts ldi ldi sts sts sts sts sts sts sts sts sts sts sts sts sts sts sts sts lds ret USIDR,r16 r16,(1< 7753C-AVR-07/09 17.3.3 SPI Slave Operation Example The following code demonstrates how to use the USI module as a SPI Slave: init: ldi sts ... SlaveSPITransfer: sts ldi sts lds sbrs rjmp lds ret USIDR,r16 r16,(1< The code is size optimized using only eight instructions (+ ret). The code example assumes that the DO is configured as output and USCK pin is configured as input in the DDR Register. The value stored in register r16 prior to the function is called is transferred to the master device, and when the transfer is completed the data received from the Master is stored back into the r16 Register. Note that the first two instructions is for initialization only and needs only to be executed once.These instructions sets Three-wire mode and positive edge USI Data Register clock. The loop is repeated until the USI Counter Overflow Flag is set. 17.3.4 Two-wire Mode The USI Two-wire mode is compliant to the Inter IC (TWI) bus protocol, but without slew rate limiting on outputs and input noise filtering. Pin names used by this mode are SCL and SDA. 132 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 17-4. Two-wire Mode Operation, Simplified Diagram VCC Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 SDA SCL HOLD SCL Two-wire Clock Control Unit SLAVE Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 SDA SCL PORTxn MASTER Figure 17-4 shows two USI units operating in Two-wire mode, one as Master and one as Slave. It is only the physical layer that is shown since the system operation is highly dependent of the communication scheme used. The main differences between the Master and Slave operation at this level, is the serial clock generation which is always done by the Master, and only the Slave uses the clock control unit. Clock generation must be implemented in software, but the shift operation is done automatically by both devices. Note that only clocking on negative edge for shifting data is of practical use in this mode. The slave can insert wait states at start or end of transfer by forcing the SCL clock low. This means that the Master must always check if the SCL line was actually released after it has generated a positive edge. Since the clock also increments the counter, a counter overflow can be used to indicate that the transfer is completed. The clock is generated by the master by toggling the USCK pin via the PORT Register. The data direction is not given by the physical layer. A protocol, like the one used by the TWI-bus, must be implemented to control the data flow. Figure 17-5. Two-wire Mode, Typical Timing Diagram SDA SCL S 1-7 ADDRESS 8 R/W 9 ACK 1-8 DATA 9 ACK 1-8 DATA 9 ACK P A B C D E F 133 7753C-AVR-07/09 Referring to the timing diagram (Figure 17-5.), a bus transfer involves the following steps: 1. The a start condition is generated by the Master by forcing the SDA low line while the SCL line is high (A). SDA can be forced low either by writing a zero to bit 7 of the Shift Register, or by setting the corresponding bit in the PORT Register to zero. Note that the USI Data Register bit must be set to one for the output to be enabled. The slave device's start detector logic (Figure 17-6.) detects the start condition and sets the USISIF Flag. The flag can generate an interrupt if necessary. 2. In addition, the start detector will hold the SCL line low after the Master has forced an negative edge on this line (B). This allows the Slave to wake up from sleep or complete its other tasks before setting up the USI Data Register to receive the address. This is done by clearing the start condition flag and reset the counter. 3. The Master set the first bit to be transferred and releases the SCL line (C). The Slave samples the data and shift it into the USI Data Register at the positive edge of the SCL clock. 4. After eight bits are transferred containing slave address and data direction (read or write), the Slave counter overflows and the SCL line is forced low (D). If the slave is not the one the Master has addressed, it releases the SCL line and waits for a new start condition. 5. If the Slave is addressed it holds the SDA line low during the acknowledgment cycle before holding the SCL line low again (i.e., the Counter Register must be set to 14 before releasing SCL at (D)). Depending of the R/W bit the Master or Slave enables its output. If the bit is set, a master read operation is in progress (i.e., the slave drives the SDA line) The slave can hold the SCL line low after the acknowledge (E). 6. Multiple bytes can now be transmitted, all in same direction, until a stop condition is given by the Master (F). Or a new start condition is given. If the Slave is not able to receive more data it does not acknowledge the data byte it has last received. When the Master does a read operation it must terminate the operation by force the acknowledge bit low after the last byte transmitted. Figure 17-6. Start Condition Detector, Logic Diagram USISIF DQ SDA CLR CLR DQ CLOCK HOLD SCL Write( USISIF) 17.3.5 Start Condition Detector The start condition detector is shown in Figure 17-6. The SDA line is delayed (in the range of 50 to 300 ns) to ensure valid sampling of the SCL line. The start condition detector is only enabled in Two-wire mode. The start condition detector is working asynchronously and can therefore wake up the processor from the Power-down sleep mode. However, the protocol used might have restrictions on the SCL hold time. Therefore, when using this feature in this case the Oscillator start-up time set by the CKSEL Fuses (see "Clock Systems and their Distribution" on page 25) must also be taken into the consideration. Refer to the USISIF bit description on page 136 for further details. 134 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 17.4 Alternative USI Usage When the USI unit is not used for serial communication, it can be set up to do alternative tasks due to its flexible design. 17.4.1 Half-duplex Asynchronous Data Transfer By utilizing the USI Data Register in Three-wire mode, it is possible to implement a more compact and higher performance UART than by software only. 4-bit Counter The 4-bit counter can be used as a stand-alone counter with overflow interrupt. Note that if the counter is clocked externally, both clock edges will generate an increment. 17.4.2 17.4.3 12-bit Timer/Counter Combining the USI 4-bit counter and Timer/Counter0 allows them to be used as a 12-bit counter. Edge Triggered External Interrupt By setting the counter to maximum value (F) it can function as an additional external interrupt. The Overflow Flag and Interrupt Enable bit are then used for the external interrupt. This feature is selected by the USICS1 bit. Software Interrupt The counter overflow interrupt can be used as a software interrupt triggered by a clock strobe. 17.4.4 17.4.5 17.5 17.5.1 Register Descriptions USIDR - USI Data Register Bit 0x0F (0x2F) Read/Write Initial Value 7 MSB R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 6 5 4 3 2 1 0 LSB R/W 0 USIDR When accessing the USI Data Register (USIDR) the Serial Register can be accessed directly. If a serial clock occurs at the same cycle the register is written, the register will contain the value written and no shift is performed. A (left) shift operation is performed depending of the USICS1..0 bits setting. The shift operation can be controlled by an external clock edge, by a Timer/Counter0 Compare Match, or directly by software using the USICLK strobe bit. Note that even when no wire mode is selected (USIWM1..0 = 0) both the external data input (DI/SDA) and the external clock input (USCK/SCL) can still be used by the USI Data Register. The output pin in use, DO or SDA depending on the wire mode, is connected via the output latch to the most significant bit (bit 7) of the Data Register. The output latch is open (transparent) during the first half of a serial clock cycle when an external clock source is selected (USICS1 = 1), and constantly open when an internal clock source is used (USICS1 = 0). The output will be changed immediately when a new MSB written as long as the latch is open. The latch ensures that data input is sampled and data output is changed on opposite clock edges. Note that the corresponding Data Direction Register to the pin must be set to one for enabling data output from the USI Data Register. 135 7753C-AVR-07/09 17.5.2 USIBR - USI Buffer Register Bit 0x10 (0x30) Read/Write Initial Value 7 MSB R 0 R 0 R 0 R 0 R 0 R 0 R 0 6 5 4 3 2 1 0 LSB R 0 USIBR The content of the Serial Register is loaded to the USI Buffer Register when the transfer is completed, and instead of accessing the USI Data Register (the Serial Register) the USI Data Buffer can be accessed when the CPU reads the received data. This gives the CPU time to handle other program tasks too as the controlling of the USI is not so timing critical. The USI flags as set same as when reading the USIDR register. 17.5.3 USISR - USI Status Register Bit 0x0E (0x2E) Read/Write Initial Value 7 USISIF R/W 0 6 USIOIF R/W 0 5 USIPF R/W 0 4 USIDC R 0 3 USICNT3 R/W 0 2 USICNT2 R/W 0 1 USICNT1 R/W 0 0 USICNT0 R/W 0 USISR The Status Register contains Interrupt Flags, line Status Flags and the counter value. * Bit 7 - USISIF: Start Condition Interrupt Flag When Two-wire mode is selected, the USISIF Flag is set (to one) when a start condition is detected. When output disable mode or Three-wire mode is selected and (USICSx = 0b11 & USICLK = 0) or (USICS = 0b10 & USICLK = 0), any edge on the SCK pin sets the flag. An interrupt will be generated when the flag is set while the USISIE bit in USICR and the Global Interrupt Enable Flag are set. The flag will only be cleared by writing a logical one to the USISIF bit. Clearing this bit will release the start detection hold of USCL in Two-wire mode. A start condition interrupt will wakeup the processor from all sleep modes. * Bit 6 - USIOIF: Counter Overflow Interrupt Flag This flag is set (one) when the 4-bit counter overflows (i.e., at the transition from 15 to 0). An interrupt will be generated when the flag is set while the USIOIE bit in USICR and the Global Interrupt Enable Flag are set. The flag will only be cleared if a one is written to the USIOIF bit. Clearing this bit will release the counter overflow hold of SCL in Two-wire mode. A counter overflow interrupt will wake up the processor from Idle sleep mode. * Bit 5 - USIPF: Stop Condition Flag When Two-wire mode is selected, the USIPF Flag is set (one) when a stop condition is detected. The flag is cleared by writing a one to this bit. Note that this is not an Interrupt Flag. This signal is useful when implementing Two-wire bus master arbitration. * Bit 4 - USIDC: Data Output Collision This bit is logical one when bit 7 in the USI Data Register differs from the physical pin value. The flag is only valid when Two-wire mode is used. This signal is useful when implementing Two-wire bus master arbitration. * Bits 3:0 - USICNT3..0: Counter Value These bits reflect the current 4-bit counter value. The 4-bit counter value can directly be read or written by the CPU. 136 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 The 4-bit counter increments by one for each clock generated either by the external clock edge detector, by a Timer/Counter0 Compare Match, or by software using USICLK or USITC strobe bits. The clock source depends of the setting of the USICS1..0 bits. For external clock operation a special feature is added that allows the clock to be generated by writing to the USITC strobe bit. This feature is enabled by write a one to the USICLK bit while setting an external clock source (USICS1 = 1). Note that even when no wire mode is selected (USIWM1..0 = 0) the external clock input (USCK/SCL) are can still be used by the counter. 17.5.4 USICR - USI Control Register Bit 0x0D (0x2D) Read/Write Initial Value 7 USISIE R/W 0 6 USIOIE R/W 0 5 USIWM1 R/W 0 4 USIWM0 R/W 0 3 USICS1 R/W 0 2 USICS0 R/W 0 1 USICLK W 0 0 USITC W 0 USICR The Control Register includes interrupt enable control, wire mode setting, Clock Select setting, and clock strobe. * Bit 7 - USISIE: Start Condition Interrupt Enable Setting this bit to one enables the Start Condition detector interrupt. If there is a pending interrupt when the USISIE and the Global Interrupt Enable Flag is set to one, this will immediately be executed. Refer to the USISIF bit description on page 136 for further details. * Bit 6 - USIOIE: Counter Overflow Interrupt Enable Setting this bit to one enables the Counter Overflow interrupt. If there is a pending interrupt when the USIOIE and the Global Interrupt Enable Flag is set to one, this will immediately be executed. Refer to the USIOIF bit description on page 136 for further details. * Bit 5:4 - USIWM1:0: Wire Mode These bits set the type of wire mode to be used. Basically only the function of the outputs are affected by these bits. Data and clock inputs are not affected by the mode selected and will always have the same function. The counter and USI Data Register can therefore be clocked externally, and data input sampled, even when outputs are disabled. The relations between USIWM1:0 and the USI operation is summarized in Table 17-1. 137 7753C-AVR-07/09 Table 17-1. USIWM1 0 Relations between USIWM1..0 and the USI Operation USIWM0 Description 0 Outputs, clock hold, and start detector disabled. Port pins operates as normal. Three-wire mode. Uses DO, DI, and USCK pins. The Data Output (DO) pin overrides the corresponding bit in the PORT Register in this mode. However, the corresponding DDR bit still controls the data direction. When the port pin is set as input the pins pull-up is controlled by the PORT bit. The Data Input (DI) and Serial Clock (USCK) pins do not affect the normal port operation. When operating as master, clock pulses are software generated by toggling the PORT Register, while the data direction is set to output. The USITC bit in the USICR Register can be used for this purpose. Two-wire mode. Uses SDA (DI) and SCL (USCK) pins(1). The Serial Data (SDA) and the Serial Clock (SCL) pins are bi-directional and uses open-collector output drives. The output drivers are enabled by setting the corresponding bit for SDA and SCL in the DDR Register. When the output driver is enabled for the SDA pin, the output driver will force the line SDA low if the output of the USI Data Register or the corresponding bit in the PORT Register is zero. Otherwise the SDA line will not be driven (i.e., it is released). When the SCL pin output driver is enabled the SCL line will be forced low if the corresponding bit in the PORT Register is zero, or by the start detector. Otherwise the SCL line will not be driven. The SCL line is held low when a start detector detects a start condition and the output is enabled. Clearing the Start Condition Flag (USISIF) releases the line. The SDA and SCL pin inputs is not affected by enabling this mode. Pull-ups on the SDA and SCL port pin are disabled in Two-wire mode. Two-wire mode. Uses SDA and SCL pins. Same operation as for the Two-wire mode described above, except that the SCL line is also held low when a counter overflow occurs, and is held low until the Counter Overflow Flag (USIOIF) is cleared. 0 1 1 0 1 1 Note: 1. The DI and USCK pins are renamed to Serial Data (SDA) and Serial Clock (SCL) respectively to avoid confusion between the modes of operation. * Bit 3:2 - USICS1:0: Clock Source Select These bits set the clock source for the USI Data Register and counter. The data output latch ensures that the output is changed at the opposite edge of the sampling of the data input (DI/SDA) when using external clock source (USCK/SCL). When software strobe or Timer/Counter0 Compare Match clock option is selected, the output latch is transparent and therefore the output is changed immediately. Clearing the USICS1:0 bits enables software strobe option. When using this option, writing a one to the USICLK bit clocks both the USI Data Register and the counter. For external clock source (USICS1 = 1), the USICLK bit is no longer used as a strobe, but selects between external clocking and software clocking by the USITC strobe bit. Table 17-2 on page 139 shows the relationship between the USICS1..0 and USICLK setting and clock source used for the USI Data Register and the 4-bit counter. 138 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 17-2. USICS1 0 0 0 1 1 1 1 Relations between the USICS1..0 and USICLK Setting USICS0 0 0 1 0 1 0 1 USICLK 0 1 X 0 0 1 1 USI Data Register Clock Source No Clock Software clock strobe (USICLK) Timer/Counter0 Compare Match External, positive edge External, negative edge External, positive edge External, negative edge 4-bit Counter Clock Source No Clock Software clock strobe (USICLK) Timer/Counter0 Compare Match External, both edges External, both edges Software clock strobe (USITC) Software clock strobe (USITC) * Bit 1 - USICLK: Clock Strobe Writing a one to this bit location strobes the USI Data Register to shift one step and the counter to increment by one, provided that the USICS1..0 bits are set to zero and by doing so the software clock strobe option is selected. The output will change immediately when the clock strobe is executed, i.e., in the same instruction cycle. The value shifted into the USI Data Register is sampled the previous instruction cycle. The bit will be read as zero. When an external clock source is selected (USICS1 = 1), the USICLK function is changed from a clock strobe to a Clock Select Register. Setting the USICLK bit in this case will select the USITC strobe bit as clock source for the 4-bit counter (see Table 17-2). * Bit 0 - USITC: Toggle Clock Port Pin Writing a one to this bit location toggles the USCK/SCL value either from 0 to 1, or from 1 to 0. The toggling is independent of the setting in the Data Direction Register, but if the PORT value is to be shown on the pin the DDB2 must be set as output (to one). This feature allows easy clock generation when implementing master devices. The bit will be read as zero. When an external clock source is selected (USICS1 = 1) and the USICLK bit is set to one, writing to the USITC strobe bit will directly clock the 4-bit counter. This allows an early detection of when the transfer is done when operating as a master device. 17.5.5 USIPP - USI Pin Position Bit 0x11 (0x31) Read/Write Initial Value 7 R 0 6 R 0 5 R 0 4 R 0 3 R 0 2 R 0 1 R 0 0 USIPOS R/W 0 USIPP * Bits 7:1 - Res: Reserved Bits These bits are reserved bits in the ATtiny261/461/861 and always reads as zero. * Bit 0 - USIPOS: USI Pin Position Setting this bit to one changes the USI pin position. As default pins PB2..PB0 are used for the USI pin functions, but when writing this bit to one the USIPOS bit is set the USI pin functions are on pins PA2..PA0. 139 7753C-AVR-07/09 18. AC - Analog Comparator The Analog Comparator compares the input values on the selectable positive pin (AIN0, AIN1 or AIN2) and selectable negative pin (AIN0, AIN1 or AIN2). When the voltage on the positive pin is higher than the voltage on the negative pin, the Analog Comparator output, ACO, is set. The comparator can trigger a separate interrupt, exclusive to the Analog Comparator. The user can select Interrupt triggering on comparator output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown in Figure 18-1. Figure 18-1. Analog Comparator Block Diagram(2) BANDGAP REFERENCE ACBG ACM2..1 AIN0 AIN1 MUX AIN2 HSEL ADC MULTIPLEXER OUTPUT (1) Notes: 1. See Table 18-2 on page 142. 2. Refer to Figure 1-1 on page 2 and Table 12.3.2 on page 66 for Analog Comparator pin placement. 18.1 18.1.1 Register Description ACSRA - Analog Comparator Control and Status Register A Bit 0x08 (0x28) Read/Write Initial Value 7 ACD R/W 0 6 ACBG R/W 0 5 ACO R N/A 4 ACI R/W 0 3 ACIE R/W 0 2 ACME R/W 0 1 ACIS1 R/W 0 0 ACIS0 R/W 0 ACSRA * Bit 7 - ACD: Analog Comparator Disable When this bit is written logic one, the power to the Analog Comparator is switched off. This bit can be set at any time to turn off the Analog Comparator. This will reduce power consumption in Active and Idle mode. When changing the ACD bit, the Analog Comparator Interrupt must be disabled by clearing the ACIE bit in ACSRA. Otherwise an interrupt can occur when the bit is changed. * Bit 6 - ACBG: Analog Comparator Bandgap Select When this bit is set an internal 1.1V reference voltage replaces the positive input to the Analog Comparator. The selection of the internal voltage reference is done by writing the REFS2..0 bits in ADMUX register. When this bit is cleared, AIN0, AIN1 or AIN2 depending on the ACM2..0 bits is applied to the positive input of the analog comparator. 140 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 HLEV ACME ADEN ATtiny261/ATtiny461/ATtiny861 * Bit 5 - ACO: Analog Comparator Output The output of the Analog Comparator is synchronized and then directly connected to ACO. The synchronization introduces a delay of 1 - 2 clock cycles. * Bit 4 - ACI: Analog Comparator Interrupt Flag This bit is set by hardware when a comparator output event triggers the interrupt mode defined by ACIS1 and ACIS0. The Analog Comparator interrupt routine is executed if the ACIE bit is set and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag. * Bit 3 - ACIE: Analog Comparator Interrupt Enable When the ACIE bit is written logic one and the I-bit in the Status Register is set, the Analog Comparator interrupt is activated. When written logic zero, the interrupt is disabled. * Bit 2 - ACME: Analog Comparator Multiplexer Enable When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is zero), the ADC multiplexer selects the negative input to the Analog Comparator. When this bit is written logic zero, AIN1 is applied to the negative input of the Analog Comparator. For a detailed description of this bit, see "Analog Comparator Multiplexed Input" on page 142. * Bits 1, 0 - ACIS1, ACIS0: Analog Comparator Interrupt Mode Select These bits determine which comparator events that trigger the Analog Comparator interrupt. The different settings are shown in Table 18-1. Table 18-1. ACIS1 0 0 1 1 ACIS1/ACIS0 Settings ACIS0 0 1 0 1 Interrupt Mode Comparator Interrupt on Output Toggle. Reserved Comparator Interrupt on Falling Output Edge. Comparator Interrupt on Rising Output Edge. When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled by clearing its Interrupt Enable bit in the ACSR Register. Otherwise an interrupt can occur when the bits are changed. 18.2 Analog Comparator Multiplexed Input When the Analog to Digital Converter (ADC) is configured as single ended input channel, it is possible to select any of the ADC10..0 pins to replace the negative input to the Analog Comparator. The ADC multiplexer is used to select this input, and consequently, the ADC must be switched off to utilize this feature. If the Analog Comparator Multiplexer Enable bit (ACME in ADCSRB) is set and the ADC is switched off (ADEN in ADCSRA is zero), MUX5..0 in ADMUX select the input pin to replace the negative input to the Analog Comparator, as shown in Table 18-2. If ACME is cleared or ADEN is set, either AIN0, AIN1 or AIN2 is applied to the negative input to the Analog Comparator. 141 7753C-AVR-07/09 Table 18-2. ACME 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 x x x x x x Analog Comparator Multiplexed Input ADEN MUX5..0 xxxxxx xxxxxx xxxxxx xxxxxx xxxxxx xxxxxx xxxxxx 000000 000000 000000 000001 000001 000001 000010 000010 000010 000011 000011 000011 000100 000100 000100 000101 000101 000101 000110 000110 000110 000111 000111 000111 001000 001000 001000 001001 001001 001001 001010 001010 001010 ACM2..0 000 001 010 011 100 101,110,111 000 000 01x 1xx 000 01x 1xx 000 01x 1xx 000 01x 1xx 000 01x 1xx 000 01x 1xx 000 01x 1xx 000 01x 1xx 000 01x 1xx 000 01x 1xx 000 01x 1xx Positive Input AIN0 AIN0 AIN1 AIN1 AIN2 AIN2 AIN0 AIN0 AIN1 AIN2 AIN0 AIN1 AIN2 AIN0 AIN1 AIN2 AIN0 AIN1 AIN2 AIN0 AIN1 AIN2 AIN0 AIN1 AIN2 AIN0 AIN1 AIN2 AIN0 AIN1 AIN2 AIN0 AIN1 AIN2 AIN0 AIN1 AIN2 AIN0 AIN1 AIN2 Negative Input AIN1 AIN2 AIN0 AIN2 AIN0 AIN1 AIN1 ADC0 ADC0 ADC0 ADC1 ADC1 ADC1 ADC2 ADC2 ADC2 ADC3 ADC3 ADC3 ADC4 ADC4 ADC4 ADC5 ADC5 ADC5 ADC6 ADC6 ADC6 ADC7 ADC7 ADC7 ADC8 ADC8 ADC8 ADC9 ADC9 ADC9 ADC10 ADC10 ADC10 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 142 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 18.2.1 ACSRB - Analog Comparator Control and Status Register B Bit 0x09 (0x29) Read/Write Initial Value 7 HSEL R/W 0 6 HLEV R/W 0 5 R N/A 4 R 0 3 R 0 2 ACM2 R/W 0 1 ACM1 R/W 0 0 ACM0 R/W 0 ACSRB * Bit 7 - HSEL: Hysteresis Select When this bit is written logic one, the hysteresis of the Analog Comparator is switched on. The hysteresis level is selected by the HLEV bit. * Bit 6 - HLEV: Hysteresis Level When the hysteresis is enabled by the HSEL bit, the Hysteresis Level, HLEV, bit selects the hysteresis level that is either 20mV (HLEV=0) or 50mV (HLEV=1). * Bit 2:0 - ACM2:ACM0: Analog Comparator Multiplexer The Analog Comparator multiplexer bits select the positive and negative input pins of the Analog Comparator. The different settings are shown in Table 18-2. 143 7753C-AVR-07/09 19. ADC - Analog to Digital Converter 19.1 Features * * * * * * * * * * * * * * * * * * 10-bit Resolution 1.0 LSB Integral Non-linearity 2 LSB Absolute Accuracy 65 - 260 s Conversion Time Up to 15 kSPS at Maximum Resolution 11 Multiplexed Single Ended Input Channels 16 Differential input pairs 15 Differential input pairs with selectable gain Temperature sensor input channel Optional Left Adjustment for ADC Result Readout 0 - VCC ADC Input Voltage Range Selectable 1.1V / 2.56V ADC Voltage Reference Free Running or Single Conversion Mode ADC Start Conversion by Auto Triggering on Interrupt Sources Interrupt on ADC Conversion Complete Sleep Mode Noise Cancel Unipolar/ Bipolar Input Mode Input Polarity Reversal Mode 19.2 Overview The ATtiny261/461/861 features a 10-bit successive approximation ADC. The ADC is connected to a 11-channel Analog Multiplexer which allows 16 differential voltage input combinations and 11 single-ended voltage inputs constructed from the pins PA7..PA0 or PB7..PB4. The differential input is equipped with a programmable gain stage, providing amplification steps of 1x, 8x, 20x or 32x on the differential input voltage before the A/D conversion. The single-ended voltage inputs refer to 0V (GND). The ADC contains a Sample and Hold circuit which ensures that the input voltage to the ADC is held at a constant level during conversion. A block diagram of the ADC is shown in Figure 19-1. Internal reference voltages of nominally 1.1V or 2.56V are provided On-chip. The Internal reference voltage of 2.56V, can optionally be externally decoupled at the AREF (PA3) pin by a capacitor, for better noise performance. Alternatively, VCC can be used as reference voltage for single ended channels. There is also an option to use an external voltage reference and turn-off the internal voltage reference. These options are selected using the REFS2:0 bits of the ADMUX control register. 144 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 19-1. Analog to Digital Converter Block Schematic ADC CONVERSION COMPLETE IRQ 8-BIT DATA BUS ADIF ADIE 15 0 ADC CTRL. & STATUS REGISTER B (ADCSRB) REFS2 REFS1 GSEL MUX5 ADC MULTIPLEXER SELECT (ADMUX) MUX3 MUX2 MUX1 REFS0 MUX4 MUX0 ADLAR ADEN ADC CTRL. & STATUS REGISTER A (ADCSRA) ADPS2 ADPS1 ADSC ADC DATA REGISTER (ADCH/ADCL) ADATE ADIF ADPS0 PRESCALER MUX DECODER CONVERSION LOGIC VCC AREF INTERNAL 2.56/1.1V REFERENCE INTERNAL 1.18V REFERENCE AGND TEMPERATURE SENSOR ADC10 ADC9 ADC8 ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 POS. INPUT MUX CHANNEL SELECTION GAIN SELECTION SAMPLE & HOLD COMPARATOR 10-BIT DAC + SINGLE ENDED / DIFFERENTIAL SELECTION ADC MULTIPLEXER OUTPUT MUX + - GAIN AMPLIFIER NEG. INPUT MUX 19.3 Operation The ADC converts an analog input voltage to a 10-bit digital value through successive approximation. The minimum value represents GND and the maximum value represents the voltage on VCC, the voltage on the AREF pin or an internal 1.1V / 2.56V voltage reference. The voltage reference for the ADC may be selected by writing to the REFS2..0 bits in ADMUX. The VCC supply, the AREF pin or an internal 1.1V / 2.56V voltage reference may be selected as the ADC voltage reference. Optionally the internal 1.1V / 2.56V voltage reference may be decoupled by an external capacitor at the AREF pin to improve noise immunity. The analog input channel and differential gain are selected by writing to the MUX5..0 bits in ADMUX. Any of the 11 ADC input pins ADC10..0 can be selected as single ended inputs to the ADC. The positive and negative inputs to the differential gain amplifier are described in Table 19-5. If differential channels are selected, the differential gain stage amplifies the voltage difference between the selected input pair by the selected gain factor, 1x, 8x, 20x or 32x, according to the setting of the MUX5..0 bits in ADMUX and the GSEL bit in ADCSRB. This amplified value then becomes the analog input to the ADC. If single ended channels are used, the gain amplifier is bypassed altogether. ADC[9:0] 145 7753C-AVR-07/09 If the same ADC input pin is selected as both the positive and negative input to the differential gain amplifier, the remaining offset in the gain stage and conversion circuitry can be measured directly as the result of the conversion. This figure can be subtracted from subsequent conversions with the same gain setting to reduce offset error to below 1 LSW. The on-chip temperature sensor is selected by writing the code "111111" to the MUX5..0 bits in ADMUX register when the ADC11 channel is used as an ADC input. The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSRA. Voltage reference and input channel selections will not go into effect until ADEN is set. The ADC does not consume power when ADEN is cleared, so it is recommended to switch off the ADC before entering power saving sleep modes. The ADC generates a 10-bit result which is presented in the ADC Data Registers, ADCH and ADCL. By default, the result is presented right adjusted, but can optionally be presented left adjusted by setting the ADLAR bit in ADMUX. If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must be read first, then ADCH, to ensure that the content of the data registers belongs to the same conversion. Once ADCL is read, ADC access to data registers is blocked. This means that if ADCL has been read, and a conversion completes before ADCH is read, neither register is updated and the result from the conversion is lost. When ADCH is read, ADC access to the ADCH and ADCL Registers is re-enabled. The ADC has its own interrupt which can be triggered when a conversion completes. When ADC access to the data registers is prohibited between reading of ADCH and ADCL, the interrupt will trigger even if the result is lost. 19.4 Starting a Conversion A single conversion is started by writing a logical one to the ADC Start Conversion bit, ADSC. This bit stays high as long as the conversion is in progress and will be cleared by hardware when the conversion is completed. If a different data channel is selected while a conversion is in progress, the ADC will finish the current conversion before performing the channel change. Alternatively, a conversion can be triggered automatically by various sources. Auto Triggering is enabled by setting the ADC Auto Trigger Enable bit, ADATE in ADCSRA. The trigger source is selected by setting the ADC Trigger Select bits, ADTS in ADCSRB (see description of the ADTS bits for a list of the trigger sources). When a positive edge occurs on the selected trigger signal, the ADC prescaler is reset and a conversion is started. This provides a method of starting conversions at fixed intervals. If the trigger signal still is set when the conversion completes, a new conversion will not be started. If another positive edge occurs on the trigger signal during conversion, the edge will be ignored. Note that an Interrupt Flag will be set even if the specific interrupt is disabled or the Global Interrupt Enable bit in SREG is cleared. A conversion can thus be triggered without causing an interrupt. However, the Interrupt Flag must be cleared in order to trigger a new conversion at the next interrupt event. 146 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 19-2. ADC Auto Trigger Logic ADTS[2:0] PRESCALER START ADIF SOURCE 1 . . . . SOURCE n ADSC ADATE CLKADC CONVERSION LOGIC EDGE DETECTOR Using the ADC Interrupt Flag as a trigger source makes the ADC start a new conversion as soon as the ongoing conversion has finished. The ADC then operates in Free Running mode, constantly sampling and updating the ADC Data Register. The first conversion must be started by writing a logical one to the ADSC bit in ADCSRA. In this mode the ADC will perform successive conversions independently of whether the ADC Interrupt Flag, ADIF is cleared or not. If Auto Triggering is enabled, single conversions can be started by writing ADSC in ADCSRA to one. ADSC can also be used to determine if a conversion is in progress. The ADSC bit will be read as one during a conversion, independently of how the conversion was started. 19.5 Prescaling and Conversion Timing Figure 19-3. ADC Prescaler ADEN START CK Reset 7-BIT ADC PRESCALER ADPS0 ADPS1 ADPS2 ADC CLOCK SOURCE By default, the successive approximation circuitry requires an input clock frequency between 50 kHz and 200 kHz to get maximum resolution. If a lower resolution than 10 bits is needed, the input clock frequency to the ADC can be higher than 200 kHz to get a higher sample rate. The ADC module contains a prescaler, which generates an acceptable ADC clock frequency from any CPU frequency above 100 kHz. The prescaling is set by the ADPS bits in ADCSRA. 147 7753C-AVR-07/09 CK/128 CK/16 CK/32 CK/64 CK/2 CK/4 CK/8 The prescaler starts counting from the moment the ADC is switched on by setting the ADEN bit in ADCSRA. The prescaler keeps running for as long as the ADEN bit is set, and is continuously reset when ADEN is low. When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion starts at the following rising edge of the ADC clock cycle. A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is switched on (ADEN in ADCSRA is set) takes 25 ADC clock cycles in order to initialize the analog circuitry. The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conversion and 14.5 ADC clock cycles after the start of an first conversion. When a conversion is complete, the result is written to the ADC Data Registers, and ADIF is set. In Single Conversion mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a new conversion will be initiated on the first rising ADC clock edge. When Auto Triggering is used, the prescaler is reset when the trigger event occurs. This assures a fixed delay from the trigger event to the start of conversion. In this mode, the sample-and-hold takes place two ADC clock cycles after the rising edge on the trigger source signal. Three additional CPU clock cycles are used for synchronization logic. In Free Running mode, a new conversion will be started immediately after the conversion completes, while ADSC remains high. For a summary of conversion times, see Table 19-1. Figure 19-4. ADC Timing Diagram, First Conversion (Single Conversion Mode) First Conversion Next Conversion Cycle Number 1 2 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1 2 3 ADC Clock ADEN ADSC ADIF ADCH ADCL Sign and MSB of Result LSB of Result MUX and REFS Update Sample & Hold Conversion Complete MUX and REFS Update Figure 19-5. ADC Timing Diagram, Single Conversion One Conversion Next Conversion Cycle Number ADC Clock ADSC ADIF ADCH ADCL 1 2 3 4 5 6 7 8 9 10 11 12 13 1 2 3 Sign and MSB of Result LSB of Result Sample & Hold MUX and REFS Update Conversion Complete MUX and REFS Update 148 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 19-6. ADC Timing Diagram, Auto Triggered Conversion One Conversion Next Conversion Cycle Number ADC Clock Trigger Source ADATE ADIF ADCH ADCL 1 2 3 4 5 6 7 8 9 10 11 12 13 1 2 Sign and MSB of Result LSB of Result Sample & Hold MUX and REFS Update Conversion Complete Prescaler Reset Prescaler Reset Figure 19-7. ADC Timing Diagram, Free Running Conversion One Conversion 11 12 13 Next Conversion 1 2 3 4 Cycle Number ADC Clock ADSC ADIF ADCH ADCL Sign and MSB of Result LSB of Result Conversion Complete Sample & Hold MUX and REFS Update Table 19-1. Condition ADC Conversion Time Sample & Hold (Cycles from Start of Conversion) 13.5 1.5 2 Total Conversion Time (Cycles) 25 13 13.5 First conversion Normal conversions Auto Triggered conversions 19.6 Changing Channel or Reference Selection The MUX5:0 and REFS2:0 bits in the ADMUX Register are single buffered through a temporary register to which the CPU has random access. This ensures that the channels and reference selection only takes place at a safe point during the conversion. The channel and reference selection is continuously updated until a conversion is started. Once the conversion starts, the channel and reference selection is locked to ensure a sufficient sampling time for the ADC. Continuous updating resumes in the last ADC clock cycle before the conversion completes (ADIF in ADCSRA is set). 149 7753C-AVR-07/09 Note that the conversion starts on the following rising ADC clock edge after ADSC is written. The user is thus advised not to write new channel or reference selection values to ADMUX until one ADC clock cycle after ADSC is written. If Auto Triggering is used, the exact time of the triggering event can be indeterministic. Special care must be taken when updating the ADMUX Register, in order to control which conversion will be affected by the new settings. If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the ADMUX Register is changed in this period, the user cannot tell if the next conversion is based on the old or the new settings. ADMUX can be safely updated in the following ways: a. When ADATE or ADEN is cleared. b. c. During conversion, minimum one ADC clock cycle after the trigger event. After a conversion, before the Interrupt Flag used as trigger source is cleared. When updating ADMUX in one of these conditions, the new settings will affect the next ADC conversion. 19.6.1 ADC Input Channels When changing channel selections, the user should observe the following guidelines to ensure that the correct channel is selected: In Single Conversion mode, always select the channel before starting the conversion. The channel selection may be changed one ADC clock cycle after writing one to ADSC. However, the simplest method is to wait for the conversion to complete before changing the channel selection. In Free Running mode, always select the channel before starting the first conversion. The channel selection may be changed one ADC clock cycle after writing one to ADSC. However, the simplest method is to wait for the first conversion to complete, and then change the channel selection. Since the next conversion has already started automatically, the next result will reflect the previous channel selection. Subsequent conversions will reflect the new channel selection. 19.6.2 ADC Voltage Reference The voltage reference for the ADC (VREF) indicates the conversion range for the ADC. Single ended channels that exceed VREF will result in codes close to 0x3FF. VREF can be selected as either VCC, or internal 1.1V / 2.56V voltage reference, or external AREF pin. The first ADC conversion result after switching voltage reference source may be inaccurate, and the user is advised to discard this result. 150 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 19.7 ADC Noise Canceler The ADC features a noise canceler that enables conversion during sleep mode to reduce noise induced from the CPU core and other I/O peripherals. The noise canceler can be used with ADC Noise Reduction and Idle mode. To make use of this feature, the following procedure should be used: a. Make sure that the ADC is enabled and is not busy converting. Single Conversion mode must be selected and the ADC conversion complete interrupt must be enabled. b. c. Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the CPU has been halted. If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up the CPU and execute the ADC Conversion Complete interrupt routine. If another interrupt wakes up the CPU before the ADC conversion is complete, that interrupt will be executed, and an ADC Conversion Complete interrupt request will be generated when the ADC conversion completes. The CPU will remain in active mode until a new sleep command is executed. Note that the ADC will not be automatically turned off when entering other sleep modes than Idle mode and ADC Noise Reduction mode. The user is advised to write zero to ADEN before entering such sleep modes to avoid excessive power consumption. 19.7.1 Analog Input Circuitry The analog input circuitry for single ended channels is illustrated in Figure 19-8. An analog source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regardless of whether that channel is selected as input for the ADC. When the channel is selected, the source must drive the S/H capacitor through the series resistance (combined resistance in the input path). The ADC is optimized for analog signals with an output impedance of approximately 10 k or less. If such a source is used, the sampling time will be negligible. If a source with higher impedance is used, the sampling time will depend on how long time the source needs to charge the S/H capacitor, with can vary widely. The user is recommended to only use low impedent sources with slowly varying signals, since this minimizes the required charge transfer to the S/H capacitor. Signal components higher than the Nyquist frequency (fADC/2) should not be present to avoid distortion from unpredictable signal convolution. The user is advised to remove high frequency components with a low-pass filter before applying the signals as inputs to the ADC. Figure 19-8. Analog Input Circuitry IIH ADCn 1..100 k CS/H= 14 pF IIL VCC/2 151 7753C-AVR-07/09 19.7.2 Analog Noise Canceling Techniques Digital circuitry inside and outside the device generates EMI which might affect the accuracy of analog measurements. If conversion accuracy is critical, the noise level can be reduced by applying the following techniques: a. Keep analog signal paths as short as possible. Make sure analog tracks run over the analog ground plane, and keep them well away from high-speed switching digital tracks. b. c. Use the ADC noise canceler function to reduce induced noise from the CPU. If any port pins are used as digital outputs, it is essential that these do not switch while a conversion is in progress. 19.7.3 ADC Accuracy Definitions An n-bit single-ended ADC converts a voltage linearly between GND and V REF in 2 n steps (LSBs). The lowest code is read as 0, and the highest code is read as 2n-1. Several parameters describe the deviation from the ideal behavior: * Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition (at 0.5 LSB). Ideal value: 0 LSB. Figure 19-9. Offset Error Output Code Ideal ADC Actual ADC Offset Error VREF Input Voltage * Gain Error: After adjusting for offset, the Gain Error is found as the deviation of the last transition (0x3FE to 0x3FF) compared to the ideal transition (at 1.5 LSB below maximum). Ideal value: 0 LSB 152 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 19-10. Gain Error Output Code Gain Error Ideal ADC Actual ADC VREF Input Voltage * Integral Non-linearity (INL): After adjusting for offset and gain error, the INL is the maximum deviation of an actual transition compared to an ideal transition for any code. Ideal value: 0 LSB. Figure 19-11. Integral Non-linearity (INL) Output Code * Differential Non-linearity (DNL): The maximum deviation of the actual code width (the interval between two adjacent transitions) from the ideal code width (1 LSB). Ideal value: 0 LSB. INL Ideal ADC Actual ADC VREF Input Voltage 153 7753C-AVR-07/09 Figure 19-12. Differential Non-linearity (DNL) Output Code 0x3FF 1 LSB DNL 0x000 0 VREF Input Voltage * Quantization Error: Due to the quantization of the input voltage into a finite number of codes, a range of input voltages (1 LSB wide) will code to the same value. Always 0.5 LSB. * Absolute Accuracy: The maximum deviation of an actual (unadjusted) transition compared to an ideal transition for any code. This is the compound effect of offset, gain error, differential error, non-linearity, and quantization error. Ideal value: 0.5 LSB. 19.8 ADC Conversion Result After the conversion is complete (ADIF is high), the conversion result can be found in the ADC Result Registers (ADCL, ADCH). The form of the conversion result depends on the type of the conversion as there are three types of conversions: single ended conversion, unipolar differential conversion and bipolar differential conversion. 19.8.1 Single Ended Conversion For single ended conversion, the result is V IN 1024 ADC = ---------------------------V REF where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see Table 19-4 on page 157 and Table 19-5 on page 158). 0x000 represents analog ground, and 0x3FF represents the selected voltage reference minus one LSB. The result is presented in one-sided form, from 0x3FF to 0x000. 19.8.2 Unipolar Differential Conversion If differential channels and an unipolar input mode are used, the result is ( V POS - V NEG ) 1024 ADC = ---------------------------------------------------------- GAIN V REF where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin, and VREF the selected voltage reference (see Table 19-4 on page 157 and Table 19-5 on page 158). The voltage on the positive pin must always be larger than the voltage on the negative pin or otherwise the voltage difference is saturated to zero. The result is presented in one-sided form, from 0x000 (0d) to 0x3FF (+1023d). The GAIN is either 1x, 8x, 20x or 32x. 154 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 19.8.3 Bipolar Differential Conversion As default the ADC converter operates in the unipolar input mode, but the bipolar input mode can be selected by writing the BIN bit in the ADCSRB to one. In the bipolar input mode two-sided voltage differences are allowed and thus the voltage on the negative input pin can also be larger than the voltage on the positive input pin. If differential channels and a bipolar input mode are used, the result is ( V POS - V NEG ) 512 ADC = ------------------------------------------------------- GAIN V REF where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin, and VREF the selected voltage reference. The result is presented in two's complement form, from 0x200 (-512d) through 0x000 (+0d) to 0x1FF (+511d). The GAIN is either 1x, 8x, 20x or 32x. However, if the signal is not bipolar by nature (9 bits + sign as the 10th bit), this scheme loses one bit of the converter dynamic range. Then, if the user wants to perform the conversion with the maximum dynamic range, the user can perform a quick polarity check of the result and use the unipolar differential conversion with selectable differential input pair. When the polarity check is performed, it is sufficient to read the MSB of the result (ADC9 in ADCH). If the bit is one, the result is negative, and if this bit is zero, the result is positive. 19.9 Temperature Measurement The temperature measurement is based on an on-chip temperature sensor that is coupled to a single ended ADC input. MUX[4..0] bits in ADMUX register enables the temperature sensor. The internal 1.1V voltage reference must also be selected for the ADC voltage reference source in the temperature sensor measurement. When the temperature sensor is enabled, the ADC converter can be used in single conversion mode to measure the voltage over the temperature sensor. The measured voltage has a linear relationship to the temperature as described in Table 19-2. The voltage sensitivity is approximately 1LSB/C and the accuracy of the temperature measurement is 10C using manufacturing calibration values (TS_GAIN, TS_OFFSET). The values described in Table 19-2 are typical values. However, due to the process variation the temperature sensor output varies from one chip to another. Table 19-2. Temperature vs. Sensor Output Voltage (Typical Case): Example ADC Values -40C 0x00F6 +25 C 0x0144 +125 C 0c01B8 Temperature / C 155 7753C-AVR-07/09 19.9.1 Manufacturing Calibration Calibration values determined during test are available in the signature row. The temperature in degrees Celsius can be calculated using the formula: ( [ ADCH << 8 I ADCL ] - 273 + 25 - TS_OFFSET ) x 128 T = --------------------------------------------------------------------------------------------------------------------------------------------------------------------- + 25 TS_GAIN Where: a. ADCH & ADCL are the ADC data registers, b. is the temperature sensor gain c. TS_OFFSET is the temperature sensor offset correction term TS_GAIN is the unsigned fixed point 8-bit temperature sensor gain factor in 1/128th units stored in the signature row. TS_OFFSET is the signed twos complement temperature sensor offset reading stored in the signature row. The table below summarizes the parameter signature row address vs product. Table 19-3. Parameter Signature Row Address vs. Product ATtiny261 ATtiny461 0x05 0x07 ATtiny861 0x05 0x07 0x1F 0x1E TS_OFFSET TS_GAIN The following code example allows to read Signature Row data .equ TS_GAIN = 0x0007 .equ TS_OFFSET = 0x0005 LDI R30,LOW(TS_GAIN) LDI R31,HIGH (TS_GAIN) RCALL Read_signature_row MOV R17,R16 LDI R30,LOW(TS_OFFSET) LDI R31,HIGH (TS_OFFSET) RCALL Read_signature_row ; R16 holds TS_OFFSET and R17 holds TS_GAIN Read_signature_row: IN R16,SPMCSR SBRC R16,SPMEN ; Wait for SPMEN ready ; Exit loop here when SPMCSR is free ; Save R16 result RJMP Read_signature_row LDI R16,((1< ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 19.10 Register Description 19.10.1 ADMUX - ADC Multiplexer Selection Register Bit 0x07 (0x27) Read/Write Initial Value 7 REFS1 R/W 0 6 REFS0 R/W 0 5 ADLAR R/W 0 4 MUX4 R/W 0 3 MUX3 R/W 0 2 MUX2 R/W 0 1 MUX1 R/W 0 0 MUX0 R/W 0 ADMUX * Bit 7:6 - REFS1:REFS0: Voltage Reference Selection Bits These bits and the REFS2 bit from the ADC Control and Status Register B (ADCSRB) select the voltage reference for the ADC, as shown in Table 19-4. If these bits are changed during a conversion, the change will not go in effect until this conversion is complete (ADIF in ADCSR is set). Whenever these bits are changed, the next conversion will take 25 ADC clock cycles. If active channels are used, using AVCC or an external AREF higher than (AVCC - 1V) is not recommended, as this will affect ADC accuracy. The internal voltage reference options may not be used if an external voltage is being applied to the AREF pin. Table 19-4. REFS2 X X 0 0 1 1 Voltage Reference Selections for ADC REFS1 0 0 1 1 1 1 REFS0 0 1 0 1 0 1 Voltage Reference (VREF) Selection VCC used as Voltage Reference, disconnected from AREF. External Voltage Reference at AREF pin, Internal Voltage Reference turned off. Internal 1.1V Voltage Reference. Reserved. Internal 2.56V Voltage Reference without external bypass capacitor, disconnected from AREF. Internal 2.56V Voltage Reference with external bypass capacitor at AREF pin. * Bit 5 - ADLAR: ADC Left Adjust Result The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data Register. Write one to ADLAR to left adjust the result. Otherwise, the result is right adjusted. Changing the ADLAR bit will affect the ADC Data Register immediately, regardless of any ongoing conversions. For a complete description of this bit, see "ADCL and ADCH - The ADC Data Register" on page 161. * Bits 4:0 - MUX4:0: Analog Channel and Gain Selection Bits These bits and the MUX5 bit from the ADC Control and Status Register B (ADCSRB) select which combination of analog inputs are connected to the ADC. In case of differential input, gain selection is also made with these bits. Selecting the same pin as both inputs to the differential gain stage enables offset measurements. Selecting the single-ended channel ADC11 enables the temperature sensor. Refer to Table 19-5 for details. If these bits are changed during a conversion, the change will not go into effect until this conversion is complete (ADIF in ADCSRA is set). 157 7753C-AVR-07/09 Table 19-5. MUX5..0 000000 000001 000010 000011 000100 000101 000110 000111 001000 001001 001010 001011 001100 001101 001110 001111 010000 010001 Input Channel Selections Single Ended Input ADC0 (PA0) ADC1 (PA1) ADC2 (PA2) ADC3 (PA4) ADC4 (PA5) ADC5 (PA6) ADC6 (PA7) ADC7 (PB4) ADC8 (PB5) ADC9 (PB6) ADC10 (PB7) ADC0 (PA0) ADC0 (PA0) NA ADC1 (PA1) ADC2 (PA2) ADC2 (PA2) ADC2 (PA2) ADC3 (PA4) N/A ADC4 (PA5) ADC4 (PA5) ADC4 (PA5) ADC4 (PA5) NA ADC5 (PA6) ADC6 (PA7) ADC6 (PA7) ADC8 (PB5) ADC8 (PB5) NA ADC9 (PB6) ADC10 (PB7) ADC10 (PB7) 1.1V N/A N/A N/A 0V ADC1 (PA1) ADC1 (PA1) ADC1 (PA1) ADC1 (PA1) ADC1 (PA1) ADC3 (PA4) ADC3 (PA4) ADC3 (PA4) ADC3 (PA4) ADC5 (PA6) ADC5 (PA6) ADC5 (PA6) ADC5 (PA6) ADC5 (PA6) ADC9 (PB6) ADC9 (PB6) ADC9 (PB6) ADC9 (PB6) ADC9 (PB6) 20x 1x 20x 20x 1x 1x 20x 20x 1x 20x 1x 20x 20x 1x 20x 1x 20x 20x 1x NA NA NA Positive Differential Input Negative Differential Input Gain 010010 010011 010100 010101 010110 010111 011000 011001 011010 011011 011100 011101 011110 011111 158 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 19-5. MUX5..0 100000 100001 100010 100011 100100 100101 100110 100111 101000 101001 101010 101011 101100 101101 101110 101111 110000 110001 110010 110011 110100 110101 110110 110111 111000 111001 111010 111011 111100 111101 111110 111111 1. ADC11 (1) Input Channel Selections (Continued) Single Ended Input Positive Differential Input ADC0(PA0) ADC0(PA0) N/A ADC1(PA1 ADC1(PA1) ADC1(PA1) ADC1(PA1) N/A ADC2(PA2 ADC2(PA2) ADC2(PA2) ADC2(PA2) N/A ADC0(PA0) ADC0(PA0) ADC4(PA5) ADC4(PA5) N/A ADC5(PA6) ADC5(PA6) ADC5(PA6) ADC5(PA6) N/A ADC6(PA7) ADC6(PA7) ADC6(PA7) ADC6(PA7) N/A ADC4(PA5) ADC4(PA5) ADC0(PA0) ADC0(PA0) N/A ADC1(PA1) ADC2(PA2) ADC4(PA5) N/A ADC5(PA6) ADC6(PA7) N/A Negative Differential Input ADC1(PA1) ADC1(PA1) ADC0(PA0) ADC0(PA0) ADC2(PA2) ADC2(PA2) ADC1(PA1) ADC1(PA1) ADC0(PA0) ADC0(PA0) ADC2(PA2) ADC2(PA2) ADC5(PA6) ADC5(PA6) ADC4(PA5) ADC4(PA5) ADC6(PA7) ADC6(PA7) ADC5(PA6) ADC5(PA6) ADC4(PA5) ADC4(PA5) ADC6(PA7) ADC6(PA7) ADC0(PA0) ADC0(PA0) ADC1(PA1) ADC2(PA2) ADC4(PA5) ADC5(PA6) ADC6(PA7) N/A Gain 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 1x/8x 20x/32x 20x/32x 20x/32x 20x/32x 20x/32x N/A For temperature sensor 159 7753C-AVR-07/09 19.10.2 ADCSRA - ADC Control and Status Register A Bit 0x06 (0x26) Read/Write Initial Value 7 ADEN R/W 0 6 ADSC R/W 0 5 ADATE R/W 0 4 ADIF R/W 0 3 ADIE R/W 0 2 ADPS2 R/W 0 1 ADPS1 R/W 0 0 ADPS0 R/W 0 ADCSRA * Bit 7 - ADEN: ADC Enable Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turning the ADC off while a conversion is in progress, will terminate this conversion. * Bit 6 - ADSC: ADC Start Conversion In Single Conversion mode, write this bit to one to start each conversion. In Free Running mode, write this bit to one to start the first conversion. The first conversion after ADSC has been written after the ADC has been enabled, or if ADSC is written at the same time as the ADC is enabled, will take 25 ADC clock cycles instead of the normal 13. This first conversion performs initialization of the ADC. ADSC will read as one as long as a conversion is in progress. When the conversion is complete, it returns to zero. Writing zero to this bit has no effect. * Bit 5 - ADATE: ADC Auto Trigger Enable When this bit is written to one, Auto Triggering of the ADC is enabled. The ADC will start a conversion on a positive edge of the selected trigger signal. The trigger source is selected by setting the ADC Trigger Select bits, ADTS in ADCSRB. * Bit 4 - ADIF: ADC Interrupt Flag This bit is set when an ADC conversion completes and the data registers are updated. The ADC Conversion Complete Interrupt is executed if the ADIE bit and the I-bit in SREG are set. ADIF is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ADIF is cleared by writing a logical one to the flag. Beware that if doing a Read-Modify-Write on ADCSRA, a pending interrupt can be disabled. This also applies if the SBI and CBI instructions are used. * Bit 3 - ADIE: ADC Interrupt Enable When this bit is written to one and the I-bit in SREG is set, the ADC Conversion Complete Interrupt is activated. * Bits 2:0 - ADPS2:0: ADC Prescaler Select Bits These bits determine the division factor between the system clock frequency and the input clock to the ADC. 160 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 19-6. ADPS2 0 0 0 0 1 1 1 1 ADC Prescaler Selections ADPS1 0 0 1 1 0 0 1 1 ADPS0 0 1 0 1 0 1 0 1 Division Factor 2 2 4 8 16 32 64 128 19.10.3 19.10.3.1 ADCL and ADCH - The ADC Data Register ADLAR = 0 Bit 0x05 (0x25) 0x04 (0x24) 15 - ADC7 7 Read/Write R R Initial Value 0 0 14 - ADC6 6 R R 0 0 13 - ADC5 5 R R 0 0 12 - ADC4 4 R R 0 0 11 - ADC3 3 R R 0 0 10 - ADC2 2 R R 0 0 9 ADC9 ADC1 1 R R 0 0 8 ADC8 ADC0 0 R R 0 0 ADCH ADCL 19.10.3.2 ADLAR = 1 Bit 0x05 (0x25) 0x04 (0x24) 15 ADC9 ADC1 7 Read/Write R R Initial Value 0 0 14 ADC8 ADC0 6 R R 0 0 13 ADC7 - 5 R R 0 0 12 ADC6 - 4 R R 0 0 11 ADC5 - 3 R R 0 0 10 ADC4 - 2 R R 0 0 9 ADC3 - 1 R R 0 0 8 ADC2 - 0 R R 0 0 ADCH ADCL When an ADC conversion is complete, the result is found in these two registers. When ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently, if the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must be read first, then ADCH. The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is read from the registers. If ADLAR is set, the result is left adjusted. If ADLAR is cleared (default), the result is right adjusted. * ADC9:0: ADC Conversion Result These bits represent the result from the conversion, as detailed in "ADC Conversion Result" on page 154. 161 7753C-AVR-07/09 19.10.4 ADCSRB - ADC Control and Status Register B Bit 0x03 (0x23) Read/Write Initial Value 7 BIN R/W 0 6 GSEL R/W 0 5 R 0 4 REFS2 R/W 0 3 MUX5 R/W 0 2 ADTS2 R/W 0 1 ADTS1 R/W 0 0 ADTS0 R/W 0 ADCSRB * Bit 7- BIN: Bipolar Input Mode The gain stage is working in the unipolar mode as default, but the bipolar mode can be selected by writing the BIN bit in the ADCSRB register. In the unipolar mode only one-sided conversions are supported and the voltage on the positive input must always be larger than the voltage on the negative input. Otherwise the result is saturated to the voltage reference. In the bipolar mode two-sided conversions are supported and the result is represented in the two's complement form. In the unipolar mode the resolution is 10 bits and the bipolar mode the resolution is 9 bits + 1 sign bit. * Bits 6 - GSEL: Gain Select The Gain Select bit selects the 32x gain instead of the 20x gain and the 8x gain instead of the 1x gain when the Gain Select bit is written to one. * Bits 5 - Res: Reserved Bit This bit is a reserved bit in the ATtiny261/461/861 and will always read as zero. * Bits 4 - REFS2: Reference Selection Bit These bit selects either the voltage reference of 1.1 V or 2.56 V for the ADC, as shown in Table 19-4. If active channels are used, using AVCC or an external AREF higher than (AVCC - 1V) is not recommended, as this will affect ADC accuracy. The internal voltage reference options may not be used if an external voltage is being applied to the AREF pin. * Bits 3 - MUX5: Analog Channel and Gain Selection Bit 5 The MUX5 bit is the MSB of the Analog Channel and Gain Selection bits. Refer to Table 19-5 for details. If this bit is changed during a conversion, the change will not go into effect until this conversion is complete (ADIF in ADCSRA is set). * Bits 2:0 - ADTS2:0: ADC Auto Trigger Source If ADATE in ADCSRA is written to one, the value of these bits selects which source will trigger an ADC conversion. If ADATE is cleared, the ADTS2:0 settings will have no effect. A conversion will be triggered by the rising edge of the selected Interrupt Flag. Note that switching from a trigger source that is cleared to a trigger source that is set, will generate a positive edge on the trigger signal. If ADEN in ADCSRA is set, this will start a conversion. Switching to Free Running mode (ADTS[2:0]=0) will not cause a trigger event, even if the ADC Interrupt Flag is set. 162 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 19-7. ADTS2 0 0 0 0 1 1 1 1 ADC Auto Trigger Source Selections ADTS1 0 0 1 1 0 0 1 1 ADTS0 0 1 0 1 0 1 0 1 Trigger Source Free Running mode Analog Comparator External Interrupt Request 0 Timer/Counter0 Compare Match A Timer/Counter0 Overflow Timer/Counter0 Compare Match B Timer/Counter1 Overflow Watchdog Interrupt Request 19.10.5 DIDR0 - Digital Input Disable Register 0 Bit 0x01 (0x21) Read/Write Initial Value 7 ADC6D R/W 0 6 ADC5D R/W 0 5 ADC4D R/W 0 4 ADC3D R/W 0 3 AREFD R/W 0 2 ADC2D R/W 0 1 ADC1D R/W 0 0 ADC0D R/W 0 DIDR0 * Bits 7:4,2:0 - ADC6D:ADC0D: ADC6:0 Digital Input Disable When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN register bit will always read as zero when this bit is set. When an analog signal is applied to the ADC7:0 pin and the digital input from this pin is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer. * Bit 3 - AREFD: AREF Digital Input Disable When this bit is written logic one, the digital input buffer on the AREF pin is disabled. The corresponding PIN register bit will always read as zero when this bit is set. When an analog signal is applied to the AREF pin and the digital input from this pin is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer. 19.10.6 DIDR1 - Digital Input Disable Register 1 Bit 0x02 (0x22) Read/Write Initial Value 7 ADC10D R/W 0 6 ADC9D R/W 0 5 ADC8D R/W 0 4 ADC7D R/W 0 3 R 0 R 0 R 0 R 0 2 1 0 DIDR1 * Bits 7..4 - ADC10D..ADC7D: ADC10..7 Digital Input Disable When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN register bit will always read as zero when this bit is set. When an analog signal is applied to the ADC10:7 pin and the digital input from this pin is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer. 163 7753C-AVR-07/09 20. debugWIRE On-chip Debug System 20.1 Features * * * * * * * * * * Complete Program Flow Control Emulates All On-chip Functions, Both Digital and Analog, except RESET Pin Real-time Operation Symbolic Debugging Support (Both at C and Assembler Source Level, or for Other HLLs) Unlimited Number of Program Break Points (Using Software Break Points) Non-intrusive Operation Electrical Characteristics Identical to Real Device Automatic Configuration System High-Speed Operation Programming of Non-volatile Memories 20.2 Overview The debugWIRE On-chip debug system uses a One-wire, bi-directional interface to control the program flow, execute AVR instructions in the CPU and to program the different non-volatile memories. 20.3 Physical Interface When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unprogrammed, the debugWIRE system within the target device is activated. The RESET port pin is configured as a wire-AND (open-drain) bi-directional I/O pin with pull-up enabled and becomes the communication gateway between target and emulator. Figure 20-1. The debugWIRE Setup 1.8 - 5.5V VCC dW dW(RESET) GND Figure 20-1 shows the schematic of a target MCU, with debugWIRE enabled, and the emulator connector. The system clock is not affected by debugWIRE and will always be the clock source selected by the CKSEL Fuses. 164 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 When designing a system where debugWIRE will be used, the following observations must be made for correct operation: * Pull-Up resistor on the dW/(RESET) line must be in the range of 10k to 20 k. However, the pull-up resistor is optional. * Connecting the RESET pin directly to VCC will not work. * Capacitors inserted on the RESET pin must be disconnected when using debugWire. * All external reset sources must be disconnected. 20.4 Software Break Points debugWIRE supports Program memory Break Points by the AVR Break instruction. Setting a Break Point in AVR Studio(R) will insert a BREAK instruction in the Program memory. The instruction replaced by the BREAK instruction will be stored. When program execution is continued, the stored instruction will be executed before continuing from the Program memory. A break can be inserted manually by putting the BREAK instruction in the program. The Flash must be re-programmed each time a Break Point is changed. This is automatically handled by AVR Studio through the debugWIRE interface. The use of Break Points will therefore reduce the Flash Data retention. Devices used for debugging purposes should not be shipped to end customers. 20.5 Limitations of debugWIRE The debugWIRE communication pin (dW) is physically located on the same pin as External Reset (RESET). An External Reset source is therefore not supported when the debugWIRE is enabled. The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e., when the program in the CPU is running. When the CPU is stopped, care must be taken while accessing some of the I/O Registers via the debugger (AVR Studio). A programmed DWEN Fuse enables some parts of the clock system to be running in all sleep modes. This will increase the power consumption while in sleep. Thus, the DWEN Fuse should be disabled when debugWire is not used. 20.6 Register Description The following section describes the registers used with the debugWire. 20.6.1 DWDR - debugWire Data Register Bit 0x20 (0x40) Read/Write Initial Value R/W 0 R/W 0 R/W 0 R/W 0 7 6 5 4 3 DWDR[7:0] R/W 0 R/W 0 R/W 0 R/W 0 2 1 0 DWDR The DWDR Register provides a communication channel from the running program in the MCU to the debugger. This register is only accessible by the debugWIRE and can therefore not be used as a general purpose register in the normal operations. 165 7753C-AVR-07/09 21. Self-Programming the Flash The device provides a Self-Programming mechanism for downloading and uploading program code by the MCU itself. The Self-Programming can use any available data interface and associated protocol to read code and write (program) that code into the Program memory. The Program memory is updated in a page by page fashion. Before programming a page with the data stored in the temporary page buffer, the page must be erased. The temporary page buffer is filled one word at a time using SPM and the buffer can be filled either before the Page Erase command or between a Page Erase and a Page Write operation: Alternative 1, fill the buffer before a Page Erase * Fill temporary page buffer * Perform a Page Erase * Perform a Page Write Alternative 2, fill the buffer after Page Erase * Perform a Page Erase * Fill temporary page buffer * Perform a Page Write If only a part of the page needs to be changed, the rest of the page must be stored (for example in the temporary page buffer) before the erase, and then be re-written. When using alternative 1, the Boot Loader provides an effective Read-Modify-Write feature which allows the user software to first read the page, do the necessary changes, and then write back the modified data. If alternative 2 is used, it is not possible to read the old data while loading since the page is already erased. The temporary page buffer can be accessed in a random sequence. It is essential that the page address used in both the Page Erase and Page Write operation is addressing the same page. 21.1 Performing Page Erase by SPM To execute Page Erase, set up the address in the Z-pointer, write "00000011" to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored. The page address must be written to PCPAGE in the Z-register. Other bits in the Z-pointer will be ignored during this operation. * The CPU is halted during the Page Erase operation. 21.2 Filling the Temporary Buffer (Page Loading) To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write "00000001" to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The content of PCWORD in the Z-register is used to address the data in the temporary buffer. The temporary buffer will auto-erase after a Page Write operation or by writing the CTPB bit in SPMCSR. It is also erased after a system reset. Note that it is not possible to write more than one time to each address without erasing the temporary buffer. If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be lost. 166 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 21.3 Performing a Page Write To execute Page Write, set up the address in the Z-pointer, write "00000101" to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored. The page address must be written to PCPAGE. Other bits in the Z-pointer must be written to zero during this operation. * The CPU is halted during the Page Write operation. 21.4 Addressing the Flash During Self-Programming The Z-pointer is used to address the SPM commands. Bit ZH (R31) ZL (R30) 15 Z15 Z7 7 14 Z14 Z6 6 13 Z13 Z5 5 12 Z12 Z4 4 11 Z11 Z3 3 10 Z10 Z2 2 9 Z9 Z1 1 8 Z8 Z0 0 Since the Flash is organized in pages (see Table 22-7 on page 174), the Program Counter can be treated as having two different sections. One section, consisting of the least significant bits, is addressing the words within a page, while the most significant bits are addressing the pages. This is shown in Figure 21-1. Note that the Page Erase and Page Write operations are addressed independently. Therefore it is of major importance that the software addresses the same page in both the Page Erase and Page Write operation. The LPM instruction uses the Z-pointer to store the address. Since this instruction addresses the Flash byte-by-byte, also the LSB (bit Z0) of the Z-pointer is used. Figure 21-1. Addressing the Flash During SPM(1) BIT Z - REGISTER PCMSB PROGRAM COUNTER PCPAGE 15 ZPCMSB ZPAGEMSB 10 0 PAGEMSB PCWORD PAGE ADDRESS WITHIN THE FLASH PROGRAM MEMORY PAGE WORD ADDRESS WITHIN A PAGE PAGE INSTRUCTION WORD PCWORD[PAGEMSB:0]: 00 01 02 PAGEEND Note: 1. The different variables used in Figure 21-1 are listed in Table 22-7 on page 174. 167 7753C-AVR-07/09 21.4.1 EEPROM Write Prevents Writing to SPMCSR Note that an EEPROM write operation will block all software programming to Flash. Reading the Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It is recommended that the user checks the status bit (EEPE) in the EECR Register and verifies that the bit is cleared before writing to the SPMCSR Register. Reading the Fuse and Lock Bits from Software It is possible to read both the Fuse and Lock bits from software. To read the Lock bits, load the Z-pointer with 0x0001 and set the RFLB and SPMEN bits in SPMCSR. When an LPM instruction is executed within three CPU cycles after the RFLB and SPMEN bits are set in SPMCSR, the value of the Lock bits will be loaded in the destination register. The RFLB and SPMEN bits will auto-clear upon completion of reading the Lock bits or if no LPM instruction is executed within three CPU cycles or no SPM instruction is executed within four CPU cycles. When RFLB and SPMEN are cleared, LPM will work as described in the Instruction set Manual. Bit Rd 7 - 6 - 5 - 4 - 3 - 2 - 1 LB2 0 LB1 21.4.2 The algorithm for reading the Fuse Low byte is similar to the one described above for reading the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and set the RFLB and SPMEN bits in SPMCSR. When an LPM instruction is executed within three cycles after the RFLB and SPMEN bits are set in the SPMCSR, the value of the Fuse Low byte (FLB) will be loaded in the destination register as shown below. Refer to Table 22-5 on page 173 for a detailed description and mapping of the Fuse Low byte. Bit Rd 7 FLB7 6 FLB6 5 FLB5 4 FLB4 3 FLB3 2 FLB2 1 FLB1 0 FLB0 Similarly, when reading the Fuse High byte, load 0x0003 in the Z-pointer. When an LPM instruction is executed within three cycles after the RFLB and SPMEN bits are set in the SPMCSR, the value of the Fuse High byte (FHB) will be loaded in the destination register as shown below. Refer to Table XXX on page XXX for detailed description and mapping of the Fuse High byte. Bit Rd 7 FHB7 6 FHB6 5 FHB5 4 FHB4 3 FHB3 2 FHB2 1 FHB1 0 FHB0 Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are unprogrammed, will be read as one. 21.4.3 Preventing Flash Corruption During periods of low VCC, the Flash program can be corrupted because the supply voltage is too low for the CPU and the Flash to operate properly. These issues are the same as for board level systems using the Flash, and the same design solutions should be applied. A Flash program corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions is too low. 168 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Flash corruption can easily be avoided by following these design recommendations (one is sufficient): 1. Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can be done by enabling the internal Brown-out Detector (BOD) if the operating voltage matches the detection level. If not, an external low VCC reset protection circuit can be used. If a reset occurs while a write operation is in progress, the write operation will be completed provided that the power supply voltage is sufficient. 2. Keep the AVR core in Power-down sleep mode during periods of low VCC. This will prevent the CPU from attempting to decode and execute instructions, effectively protecting the SPMCSR Register and thus the Flash from unintentional writes. 21.4.4 Programming Time for Flash when Using SPM The calibrated RC Oscillator is used to time Flash accesses. Table 21-1 shows the typical programming time for Flash accesses from the CPU. Table 21-1. SPM Programming Time(1) Symbol Flash write (Page Erase, Page Write, and write Lock bits by SPM) Note: Min Programming Time 3.7 ms Max Programming Time 4.5 ms 1. Minimum and maximum programming time is per individual operation. 21.5 21.5.1 Register Description SPMCSR - Store Program Memory Control and Status Register The Store Program Memory Control and Status Register contains the control bits needed to control the Program memory operations. Bit 0x37 (0x57) Read/Write Initial Value 7 - R 0 6 - R 0 5 SIGRD R 0 4 CTPB R/W 0 3 RFLB R/W 0 2 PGWRT R/W 0 1 PGERS R/W 0 0 SPMEN R/W 0 SPMCSR * Bits 7:6 - Res: Reserved Bits These bits are reserved bits in the ATtiny261/461/861 and always read as zero. * Bit 5 - SIGRD: Signature Row Read If this bit is written to one at the same time as SPMEN, the next LPM instruction within three clock cycles will read a byte from the signature row into the destination register for details. An SPM instruction within four cycles after SIGRD and SPMEN are set will have no effect. * Bit 4 - CTPB: Clear Temporary Page Buffer If the CTPB bit is written while filling the temporary page buffer, the temporary page buffer will be cleared and the data will be lost. * Bit 3 - RFLB: Read Fuse and Lock Bits An LPM instruction within three cycles after RFLB and SPMEN are set in the SPMCSR Register, will read either the Lock bits or the Fuse bits (depending on Z0 in the Z-pointer) into the destination register. See "EEPROM Write Prevents Writing to SPMCSR" on page 168 for details. 169 7753C-AVR-07/09 * Bit 2 - PGWRT: Page Write If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock cycles executes Page Write, with the data stored in the temporary buffer. The page address is taken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The PGWRT bit will auto-clear upon completion of a Page Write, or if no SPM instruction is executed within four clock cycles. The CPU is halted during the entire Page Write operation. * Bit 1 - PGERS: Page Erase If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock cycles executes Page Erase. The page address is taken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The PGERS bit will auto-clear upon completion of a Page Erase, or if no SPM instruction is executed within four clock cycles. The CPU is halted during the entire Page Write operation. * Bit 0 - SPMEN: Store Program Memory Enable This bit enables the SPM instruction for the next four clock cycles. If written to one together with either CTPB, RFLB, PGWRT, or PGERS, the following SPM instruction will have a special meaning, see description above. If only SPMEN is written, the following SPM instruction will store the value in R1:R0 in the temporary page buffer addressed by the Z-pointer. The LSB of the Z-pointer is ignored. The SPMEN bit will auto-clear upon completion of an SPM instruction, or if no SPM instruction is executed within four clock cycles. During Page Erase and Page Write, the SPMEN bit remains high until the operation is completed. Writing any other combination than "10001", "01001", "00101", "00011" or "00001" in the lower five bits will have no effect. 170 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 22. Memory Programming This section describes the different methods for Programming the ATtiny261/461/861 memories. 22.1 Program And Data Memory Lock Bits The ATtiny261/461/861 provides two Lock bits which can be left unprogrammed ("1") or can be programmed ("0") to obtain the additional security listed in Table 22-2. The Lock bits can only be erased to "1" with the Chip Erase command. The ATtiny261/461/861 has no separate Boot Loader section. The SPM instruction is enabled for the whole Flash, if the SELFPROGEN fuse is programmed ("0"), otherwise it is disabled. Table 22-1. Lock Bit Byte(1) Bit No 7 6 5 4 3 2 LB2 LB1 Note: 1 0 Description - - - - - - Lock bit Lock bit Default Value 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) Lock Bit Byte 1. "1" means unprogrammed, "0" means programmed Table 22-2. Lock Bit Protection Modes(1)(2) Protection Type LB1 1 0 No memory lock features enabled. Further programming of the Flash and EEPROM is disabled in High-voltage and Serial Programming mode. The Fuse bits are locked in both Serial and High-voltage Programming mode.(1) Further programming and verification of the Flash and EEPROM is disabled in High-voltage and Serial Programming mode. The Fuse bits are locked in both Serial and High-voltage Programming mode.(1) Memory Lock Bits LB Mode 1 2 LB2 1 1 3 0 0 Notes: 1. Program the Fuse bits before programming the LB1 and LB2. 2. "1" means unprogrammed, "0" means programmed 171 7753C-AVR-07/09 22.2 Fuse Bytes The ATtiny261/461/861 has three Fuse bytes. Table 22-3, Table 22-4 and Table 22-5 describe briefly the functionality of all the fuses and how they are mapped into the Fuse bytes. Note that the fuses are read as logical zero, "0", if they are programmed. Table 22-3. Fuse Extended Byte Bit No 7 6 5 4 3 2 1 SELFPRGEN 0 Description Self-Programming Enable Default Value 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) Fuse High Byte Table 22-4. RSTDISBL(1) DWEN (2) Fuse High Byte Bit No 7 6 6 4 3 2 1 0 Description External Reset disable DebugWIRE Enable Enable Serial Program and Data Downloading Watchdog Timer always on EEPROM memory is preserved through the Chip Erase Brown-out Detector trigger level Brown-out Detector trigger level Brown-out Detector trigger level Default Value 1 (unprogrammed) 1 (unprogrammed) 0 (programmed, SPI prog. enabled) 1 (unprogrammed) 1 (unprogrammed, EEPROM not preserved) 1 (unprogrammed) 1 (unprogrammed) 1 (unprogrammed) Fuse High Byte SPIEN(3) WDTON(4) EESAVE BODLEVEL2(5) BODLEVEL1 BODLEVEL0 Notes: (5) (5) 1. See "Alternate Functions of Port B" on page 63 for description of RSTDISBL and DWEN Fuses. 2. DWEN must be unprogrammed when Lock Bit security is required. See "Program And Data Memory Lock Bits" on page 171. 3. The SPIEN Fuse is not accessible in SPI Programming mode. 4. See "WDTCR - Watchdog Timer Control Register" on page 46 for details. 5. See Table 23-4 on page 190 for BODLEVEL Fuse decoding. 6. When programming the RSTDISBL Fuse, High-voltage Serial programming has to be used to change fuses to perform further programming. 172 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 22-5. (1) Fuse Low Byte Bit No 7 6 5 4 3 2 1 0 Description Divide clock by 8 Clock Output Enable Select start-up time Select start-up time Select Clock source Select Clock source Select Clock source Select Clock source Default Value 0 (programmed) 1 (unprogrammed) 1 (unprogrammed)(3) 0 (programmed)(3) 0 (programmed)(4) 0 (programmed)(4) 1 (unprogrammed)(4) 0 (programmed)(4) Fuse Low Byte CKDIV8 CKOUT(2) SUT1 SUT0 CKSEL3 CKSEL2 CKSEL1 CKSEL0 Notes: 1. See "System Clock Prescaler" on page 32 for details. 2. The CKOUT Fuse allows the system clock to be output on PORTB5. See "Clock Output Buffer" on page 30 for details. 3. The default value of SUT1..0 results in maximum start-up time for the default clock source. See Table 7-7 on page 29 for details. 4. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8.0 MHz. See Table 7-6 on page 29 for details. The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are locked if Lock bit1 (LB1) is programmed. Program the Fuse bits before programming the Lock bits. 22.2.1 Latching of Fuses The fuse values are latched when the device enters programming mode and changes of the fuse values will have no effect until the part leaves Programming mode. This does not apply to the EESAVE Fuse which will take effect once it is programmed. The fuses are also latched on Power-up in Normal mode. 22.3 Signature Bytes All Atmel microcontrollers have a three-byte signature code which identifies the device. This code can be read in both serial and High-voltage Programming mode, also when the device is locked. The three bytes reside in a separate address space. The ATtiny261/461/861signature bytes are given in Table 22-6. Table 22-6. Device ID Signature Bytes Address Parts ATtiny261 ATtiny461 ATtiny861 0x000 0x1E 0x1E 0x1E 0x001 0x91 0x92 0x93 0x002 0x0C 0x08 0x0D 22.4 Calibration Byte Signature area of the ATtiny261/461/861 has one byte of calibration data for the internal RC Oscillator. This byte resides in the high byte of address 0x000. During reset, this byte is automatically written into the OSCCAL Register to ensure correct frequency of the calibrated RC Oscillator. 173 7753C-AVR-07/09 22.5 Reading the Signature Row from Software To read the Signature Row from software, load the Z-pointer with the signature byte address given in Table 22-6 on page 173 and set the SIGRD and SPMEN bits in SPMCSR. When an LPM instruction is executed within three CPU cycles after the SIGRD and SPMEN bits are set in SPMCSR, the signature byte value will be loaded in the destination register. The SIGRD and SPMEN bits will auto-clear upon completion of reading the Signature Row Lock bits or if no LPM instruction is executed within three CPU cycles. When SIGRD and SPMEN are cleared, LPM will work as described in the Instruction set Manual. Note: Before attempting to set SPMEN it is important to test this bit is cleared showing that the hardware is ready for a new operation. 22.6 Page Size Table 22-7. Device ATtiny261 ATtiny461 ATtiny861 No. of Words in a Page and No. of Pages in the Flash Flash Size 1K words (2K bytes) 2K words (4K bytes) 4K words (8K bytes) Page Size 16 words 32 words 32 words PCWORD PC[3:0] PC[4:0] PC[4:0] No. of Pages 64 64 128 PCPAGE PC[9:4] PC[10:5] PC[11:5] PCMSB 9 10 11 Table 22-8. Device ATtiny261 ATtiny461 ATtiny861 No. of Words in a Page and No. of Pages in the EEPROM EEPROM Size 128 bytes 256 bytes 512 bytes Page Size 2 bytes 4 bytes 4 bytes PCWORD EEA[1:0] EEA[1:0] EEA[1:0] No. of Pages 64 64 128 PCPAGE EEA[6:2] EEA[7:2] EEA[8:2] EEAMSB 6 7 8 22.7 Parallel Programming Parameters, Pin Mapping, and Commands This section describes how to parallel program and verify Flash Program memory, EEPROM Data memory, Memory Lock bits, and Fuse bits in the ATtiny261/461/861. Pulses are assumed to be at least 250 ns unless otherwise noted. 22.7.1 Signal Names In this section, some pins of the ATtiny261/461/861 are referenced by signal names describing their functionality during parallel programming, see Figure 22-1 and Table 22-9. Pins not described in the following table are referenced by pin names. The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse. The bit coding is shown in Table 22-11. When pulsing WR or OE, the command loaded determines the action executed. The different Commands are shown in Table 22-12. 174 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 22-1. Parallel Programming +5V WR XA0 XA1/BS2 PAGEL/BS1 PB0 PB1 AVCC PB2 PB3 XTAL1/PB4 OE RDY/BSY +12 V PB5 PB6 RESET GND PA7 - PA0 VCC +5V DATA Table 22-9. Pin Name Mapping Pin Name PB0 PB1 PB2 PB3 PB5 PB6 PA7-PA0 I/O I I I I I O I/O Function Write Pulse (Active low). XTAL Action Bit 0 XTAL Action Bit 1. Byte Select 2 ("0" selects low byte, "1" selects 2'nd high byte). Byte Select 1 ("0" selects low byte, "1" selects high byte). Program Memory and EEPROM Data Page Load. Output Enable (Active low). 0: Device is busy programming, 1: Device is ready for new command. Bi-directional Data bus (Output when OE is low). Signal Name in Programming Mode WR XA0 XA1/BS2 PAGEL/BS1 OE RDY/BSY DATA I/O Table 22-10. Pin Values Used to Enter Programming Mode Pin PAGEL/BS1 XA1/BS2 XA0 WR Symbol Prog_enable[3] Prog_enable[2] Prog_enable[1] Prog_enable[0] Value 0 0 0 0 Table 22-11. XA1 and XA0 Coding XA1 0 0 1 1 XA0 0 1 0 1 Action when XTAL1 is Pulsed Load Flash or EEPROM Address (High or low address byte determined by BS1). Load Data (High or Low data byte for Flash determined by BS1). Load Command No Action, Idle 175 7753C-AVR-07/09 Table 22-12. Command Byte Bit Coding Command Byte 1000 0000 0100 0000 0010 0000 0001 0000 0001 0001 0000 1000 0000 0100 0000 0010 0000 0011 Command Executed Chip Erase Write Fuse bits Write Lock bits Write Flash Write EEPROM Read Signature Bytes and Calibration byte Read Fuse and Lock bits Read Flash Read EEPROM 22.8 22.8.1 Parallel Programming Enter Programming Mode The following algorithm puts the device in parallel programming mode: 1. Apply 4.5 - 5.5V between VCC and GND. 2. Set RESET to "0" and toggle XTAL1 at least six times. 3. Set the Prog_enable pins listed in Table 22-10 on page 175 to "0000" and wait at least 100 ns. 4. Apply 11.5 - 12.5V to RESET. Any activity on Prog_enable pins within 100 ns after +12V has been applied to RESET, will cause the device to fail entering programming mode. 5. Wait at least 50 s before sending a new command. 22.8.2 Considerations for Efficient Programming The loaded command and address are retained in the device during programming. For efficient programming, the following should be considered. * The command needs only be loaded once when writing or reading multiple memory locations. * Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the EESAVE Fuse is programmed) and Flash after a Chip Erase. * Address high byte needs only be loaded before programming or reading a new 256 word window in Flash or 256 byte EEPROM. This consideration also applies to Signature bytes reading. 22.8.3 Chip Erase The Chip Erase will erase the Flash and EEPROM(1) memories plus Lock bits. The Lock bits are not reset until the program memory has been completely erased. The Fuse bits are not changed. A Chip Erase must be performed before the Flash and/or EEPROM are reprogrammed. Note: 1. The EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is programmed. 176 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Load Command "Chip Erase" 1. Set XA1, XA0 to "10". This enables command loading. 2. Set BS1 to "0". 3. Set DATA to "1000 0000". This is the command for Chip Erase. 4. Give XTAL1 a positive pulse. This loads the command. 5. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low. 6. Wait until RDY/BSY goes high before loading a new command. 22.8.4 Programming the Flash The Flash is organized in pages, see Table 22-7 on page 174. When programming the Flash, the program data is latched into a page buffer. This allows one page of program data to be programmed simultaneously. The following procedure describes how to program the entire Flash memory: A. Load Command "Write Flash" 1. Set XA1, XA0 to "10". This enables command loading. 2. Set BS1 to "0". 3. Set DATA to "0001 0000". This is the command for Write Flash. 4. Give XTAL1 a positive pulse. This loads the command. B. Load Address Low byte 1. Set XA1, XA0 to "00". This enables address loading. 2. Set BS1 to "0". This selects low address. 3. Set DATA = Address low byte (0x00 - 0xFF). 4. Give XTAL1 a positive pulse. This loads the address low byte. C. Load Data Low Byte 1. Set XA1, XA0 to "01". This enables data loading. 2. Set DATA = Data low byte (0x00 - 0xFF). 3. Give XTAL1 a positive pulse. This loads the data byte. D. Load Data High Byte 1. Set BS1 to "1". This selects high data byte. 2. Set XA1, XA0 to "01". This enables data loading. 3. Set DATA = Data high byte (0x00 - 0xFF). 4. Give XTAL1 a positive pulse. This loads the data byte. 1. E. Latch Data 2. Set BS1 to "1". This selects high data byte. 3. Give PAGEL a positive pulse. This latches the data bytes. (See Figure 22-3 for signal waveforms) F. Repeat B through E until the entire buffer is filled or until all data within the page is loaded. 177 7753C-AVR-07/09 While the lower bits in the address are mapped to words within the page, the higher bits address the pages within the FLASH. This is illustrated in Figure 22-2 on page 178. Note that if less than eight bits are required to address words in the page (pagesize < 256), the most significant bit(s) in the address low byte are used to address the page when performing a Page Write. G. Load Address High byte 1. Set XA1, XA0 to "00". This enables address loading. 2. Set BS1 to "1". This selects high address. 3. Set DATA = Address high byte (0x00 - 0xFF). 4. Give XTAL1 a positive pulse. This loads the address high byte. H. Program Page 1. Give WR a negative pulse. This starts programming of the entire page of data. RDY/BSY goes low. 2. Wait until RDY/BSY goes high (See Figure 22-3 for signal waveforms). I. Repeat B through H until the entire Flash is programmed or until all data has been programmed. J. End Page Programming 1. 1. Set XA1, XA0 to "10". This enables command loading. 2. Set DATA to "0000 0000". This is the command for No Operation. 3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals are reset. Figure 22-2. Addressing the Flash Which is Organized in Pages(1) PCMSB PROGRAM COUNTER PCPAGE PAGEMSB PCWORD PAGE ADDRESS WITHIN THE FLASH PROGRAM MEMORY PAGE WORD ADDRESS WITHIN A PAGE PAGE INSTRUCTION WORD PCWORD[PAGEMSB:0]: 00 01 02 PAGEEND Note: 1. PCPAGE and PCWORD are listed in Table 22-7 on page 174. 178 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 22-3. Programming the Flash Waveforms(1) F A DATA 0x10 B ADDR. LOW C DATA LOW D DATA HIGH E XX B ADDR. LOW C DATA LOW D DATA HIGH E XX G ADDR. HIGH H XX XA1/BS2 XA0 PAGEL/BS1 XTAL1 WR RDY/BSY RESET +12V OE Note: 1. "XX" is don't care. The letters refer to the programming description above. 22.8.5 Programming the EEPROM The EEPROM is organized in pages, see Table 22-8 on page 174. When programming the EEPROM, the program data is latched into a page buffer. This allows one page of data to be programmed simultaneously. The programming algorithm for the EEPROM data memory is as follows (refer to "Programming the Flash" on page 177 for details on Command, Address and Data loading): 1. A: Load Command "0001 0001". 2. G: Load Address High Byte (0x00 - 0xFF). 3. B: Load Address Low Byte (0x00 - 0xFF). 4. C: Load Data (0x00 - 0xFF). 5. E: Latch data (give PAGEL a positive pulse). K: Repeat 3 through 5 until the entire buffer is filled. L: Program EEPROM page 1. Set BS to "0". 2. Give WR a negative pulse. This starts programming of the EEPROM page. RDY/BSY goes low. 3. Wait until to RDY/BSY goes high before programming the next page (See Figure 22-4 for signal waveforms). 179 7753C-AVR-07/09 Figure 22-4. Programming the EEPROM Waveforms K A DATA 0x11 G ADDR. HIGH B ADDR. LOW C DATA E XX B ADDR. LOW C DATA E XX L XA1/BS2 XA0 PAGEL/BS1 XTAL1 WR RDY/BSY RESET +12V OE 22.8.6 Reading the Flash The algorithm for reading the Flash memory is as follows (refer to "Programming the Flash" on page 177 for details on Command and Address loading): 1. A: Load Command "0000 0010". 2. G: Load Address High Byte (0x00 - 0xFF). 3. B: Load Address Low Byte (0x00 - 0xFF). 4. Set OE to "0", and BS1 to "0". The Flash word low byte can now be read at DATA. 5. Set BS to "1". The Flash word high byte can now be read at DATA. 6. Set OE to "1". 22.8.7 Reading the EEPROM The algorithm for reading the EEPROM memory is as follows (refer to "Programming the Flash" on page 177 for details on Command and Address loading): 1. A: Load Command "0000 0011". 2. G: Load Address High Byte (0x00 - 0xFF). 3. B: Load Address Low Byte (0x00 - 0xFF). 4. Set OE to "0", and BS1 to "0". The EEPROM Data byte can now be read at DATA. 5. Set OE to "1". 22.8.8 Programming the Fuse Low Bits The algorithm for programming the Fuse Low bits is as follows (refer to "Programming the Flash" on page 177 for details on Command and Data loading): 1. A: Load Command "0100 0000". 2. C: Load Data Low Byte. Bit n = "0" programs and bit n = "1" erases the Fuse bit. 3. Give WR a negative pulse and wait for RDY/BSY to go high. 180 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 22.8.9 Programming the Fuse High Bits The algorithm for programming the Fuse High bits is as follows (refer to "Programming the Flash" on page 177 for details on Command and Data loading): 1. A: Load Command "0100 0000". 2. C: Load Data Low Byte. Bit n = "0" programs and bit n = "1" erases the Fuse bit. 3. Set BS1 to "1" and BS2 to "0". This selects high data byte. 4. Give WR a negative pulse and wait for RDY/BSY to go high. 5. Set BS1 to "0". This selects low data byte. 22.8.10 Programming the Extended Fuse Bits The algorithm for programming the Extended Fuse bits is as follows (refer to "Programming the Flash" on page 177 for details on Command and Data loading): 1. 1. A: Load Command "0100 0000". 2. 2. C: Load Data Low Byte. Bit n = "0" programs and bit n = "1" erases the Fuse bit. 3. 3. Set BS1 to "0" and BS2 to "1". This selects extended data byte. 4. 4. Give WR a negative pulse and wait for RDY/BSY to go high. 5. 5. Set BS2 to "0". This selects low data byte. Figure 22-5. Programming the FUSES Waveforms Write Fuse Low byte A DATA 0x40 Write Fuse high byte A C DATA XX Write Extended Fuse byte A 0x40 C DATA XX C DATA XX 0x40 XA1/BS2 XA0 PAGEL/BS1 XTAL1 WR RDY/BSY RESET +12V OE 22.8.11 Programming the Lock Bits The algorithm for programming the Lock bits is as follows (refer to "Programming the Flash" on page 177 for details on Command and Data loading): 1. A: Load Command "0010 0000". 2. C: Load Data Low Byte. Bit n = "0" programs the Lock bit. If LB mode 3 is programmed (LB1 and LB2 is programmed), it is not possible to program the Boot Lock bits by any External Programming mode. 3. Give WR a negative pulse and wait for RDY/BSY to go high. The Lock bits can only be cleared by executing Chip Erase. 181 7753C-AVR-07/09 22.8.12 Reading the Fuse and Lock Bits The algorithm for reading the Fuse and Lock bits is as follows (refer to "Programming the Flash" on page 177 for details on Command loading): 1. A: Load Command "0000 0100". 2. Set OE to "0", BS2 to "0" and BS1 to "0". The status of the Fuse Low bits can now be read at DATA ("0" means programmed). 3. Set OE to "0", BS2 to "1" and BS1 to "1". The status of the Fuse High bits can now be read at DATA ("0" means programmed). 4. Set OE to "0", BS2 to "1", and BS1 to "0". The status of the Extended Fuse bits can now be read at DATA ("0" means programmed). 5. Set OE to "0", BS2 to "0" and BS1 to "1". The status of the Lock bits can now be read at DATA ("0" means programmed). 6. Set OE to "1". Figure 22-6. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read Fuse Low Byte 0 0 Extended Fuse Byte BS2 Lock Bits 0 1 1 DATA Fuse High Byte BS2 1 BS1 22.8.13 Reading the Signature Bytes The algorithm for reading the Signature bytes is as follows (refer to "Programming the Flash" on page 177 for details on Command and Address loading): 1. A: Load Command "0000 1000". 2. B: Load Address Low Byte (0x00 - 0x02). 3. Set OE to "0", and BS to "0". The selected Signature byte can now be read at DATA. 4. Set OE to "1". 22.8.14 Reading the Calibration Byte The algorithm for reading the Calibration byte is as follows (refer to "Programming the Flash" on page 177 for details on Command and Address loading): 1. A: Load Command "0000 1000". 2. B: Load Address Low Byte, 0x00. 3. Set OE to "0", and BS1 to "1". The Calibration byte can now be read at DATA. 4. Set OE to "1". 182 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 22.9 Serial Downloading Both the Flash and EEPROM memory arrays can be programmed using the serial SPI bus while RESET is pulled to GND. The serial interface consists of pins SCK, MOSI (input) and MISO (output). After RESET is set low, the Programming Enable instruction needs to be executed first before program/erase operations can be executed. NOTE, in Table 22-13 on page 183, the pin mapping for SPI programming is listed. Not all parts use the SPI pins dedicated for the internal SPI interface. Figure 22-7. Serial Programming and Verify(1) +1.8 - 5.5V VCC MOSI MISO SCK RESET GND Notes: 1. If the device is clocked by the internal Oscillator, it is no need to connect a clock source to the CLKI pin. Table 22-13. Pin Mapping Serial Programming Symbol MOSI MISO SCK Pins PB0 PB1 PB2 I/O I O I Description Serial Data in Serial Data out Serial Clock When programming the EEPROM, an auto-erase cycle is built into the self-timed programming operation (in the Serial mode ONLY) and there is no need to first execute the Chip Erase instruction. The Chip Erase operation turns the content of every memory location in both the Program and EEPROM arrays into 0xFF. Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high periods for the serial clock (SCK) input are defined as follows: Low: > 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz High: > 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz 183 7753C-AVR-07/09 22.9.1 Serial Programming Algorithm When writing serial data to the ATtiny261/461/861, data is clocked on the rising edge of SCK. When reading data from the ATtiny261/461/861, data is clocked on the falling edge of SCK. See Figure 23-6 and Figure 23-7 for timing details. To program and verify the ATtiny261/461/861 in the Serial Programming mode, the following sequence is recommended (see four byte instruction formats in Table 22-15): 1. Power-up sequence: Apply power between VCC and GND while RESET and SCK are set to "0". In some systems, the programmer can not guarantee that SCK is held low during power-up. In this case, RESET must be given a positive pulse of at least two CPU clock cycles duration after SCK has been set to "0". 2. Wait for at least 20 ms and enable serial programming by sending the Programming Enable serial instruction to pin MOSI. 3. The serial programming instructions will not work if the communication is out of synchronization. When in sync. the second byte (0x53), will echo back when issuing the third byte of the Programming Enable instruction. Whether the echo is correct or not, all four bytes of the instruction must be transmitted. If the 0x53 did not echo back, give RESET a positive pulse and issue a new Programming Enable command. 4. The Flash is programmed one page at a time. The memory page is loaded one byte at a time by supplying the 5 LSB of the address and data together with the Load Program memory Page instruction. To ensure correct loading of the page, the data low byte must be loaded before data high byte is applied for a given address. The Program memory Page is stored by loading the Write Program memory Page instruction with the 6 MSB of the address. If polling (RDY/BSY) is not used, the user must wait at least tWD_FLASH before issuing the next page. (See Table 22-14.) Accessing the serial programming interface before the Flash write operation completes can result in incorrect programming. 5. A: The EEPROM array is programmed one byte at a time by supplying the address and data together with the appropriate Write instruction. An EEPROM memory location is first automatically erased before new data is written. If polling (RDY/BSY) is not used, the user must wait at least tWD_EEPROM before issuing the next byte. (See Table 22-14.) In a chip erased device, no 0xFFs in the data file(s) need to be programmed. B: The EEPROM array is programmed one page at a time. The Memory page is loaded one byte at a time by supplying the 2 LSB of the address and data together with the Load EEPROM Memory Page instruction. The EEPROM Memory Page is stored by loading the Write EEPROM Memory Page Instruction with the 6 MSB of the address. When using EEPROM page access only byte locations loaded with the Load EEPROM Memory Page instruction is altered. The remaining locations remain unchanged. If polling (RDY/BSY) is not used, the used must wait at least tWD_EEPROM before issuing the next page (See Table 22-8). In a chip erased device, no 0xFF in the data file(s) need to be programmed. 6. Any memory location can be verified by using the Read instruction which returns the content at the selected address at serial output MISO. 7. At the end of the programming session, RESET can be set high to commence normal operation. 8. Power-off sequence (if needed): Set RESET to "1". Turn VCC power off. 184 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 22-14. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location Symbol tWD_FLASH tWD_EEPROM tWD_ERASE tWD_FUSE Minimum Wait Delay 4.5 ms 4.0 ms 4.0 ms 4.5 ms 22.9.2 Serial Programming Instruction set Table 22-15 on page 185 and Figure 22-8 on page 186 describes the Instruction set. Table 22-15. Serial Programming Instruction Set Instruction Format Instruction/Operation Programming Enable Chip Erase (Program Memory/EEPROM) Poll RDY/BSY Load Instructions Load Extended Address byte(1) Load Program Memory Page, High byte Load Program Memory Page, Low byte Load EEPROM Memory Page (page access) Read Instructions Read Program Memory, High byte Read Program Memory, Low byte Read EEPROM Memory Read Lock bits Read Signature Byte Read Fuse bits Read Fuse High bits Read Extended Fuse Bits Read Calibration Byte Write Instructions(6) Write Program Memory Page Write EEPROM Memory Write EEPROM Memory Page (page access) Write Lock bits $4C $C0 $C2 $AC adr MSB $00 $00 $E0 adr LSB 00aa aaaa 00aa aa00 $00 $00 data byte in $00 data byte in $28 $20 $A0 $58 $30 $50 $58 $50 $38 adr MSB adr MSB $00 $00 $00 $00 $08 $08 $00 adr LSB adr LSB 00aa aaaa $00 0000 000aa $00 $00 $00 $00 high data byte out low data byte out data byte out data byte out data byte out data byte out data byte out data byte out data byte out $4D $48 $40 $C1 $00 adr MSB adr MSB $00 Extended adr adr LSB adr LSB 0000 000aa $00 high data byte in low data byte in data byte in Byte 1 $AC $AC $F0 Byte 2 $53 $80 $00 Byte 3 $00 $00 $00 Byte4 $00 $00 data byte out 185 7753C-AVR-07/09 Table 22-15. Serial Programming Instruction Set (Continued) Instruction Format Instruction/Operation Write Fuse bits Write Fuse High bits Write Extended Fuse Bits Notes: 1. 2. 3. 4. 5. 6. 7. Byte 1 $AC $AC $AC Byte 2 $A0 $A8 $A4 Byte 3 $00 $00 $00 Byte4 data byte in data byte in data byte in Not all instructions are applicable for all parts. a = address Bits are programmed `0', unprogrammed `1'. To ensure future compatibility, unused Fuses and Lock bits should be unprogrammed (`1'). Refer to the corresponding section for Fuse and Lock bits, Calibration and Signature bytes and Page size. Instructions accessing program memory use a word address. This address may be random within the page range. See http://www.atmel.com/avr for Application Notes regarding programming and programmers. If the LSB in RDY/BSY data byte out is `1', a programming operation is still pending. Wait until this bit returns `0' before the next instruction is carried out. Within the same page, the low data byte must be loaded prior to the high data byte. After data is loaded to the page buffer, program the EEPROM page, see Figure 22-8 on page 186. Figure 22-8. Serial Programming Instruction example Serial Programming Instruction Load Program Memory Page (High/Low Byte)/ Load EEPROM Memory Page (page access) Write Program Memory Page/ Write EEPROM Memory Page Byte 1 Byte 2 A Adr MSB Bit 15 B Byte 3 Adr LSB 0 Byte 4 Byte 1 Byte 2 Adr MSB Bit 15 B Byte 3 Adr LSB r B 0 Byte 4 Page Buffer Page Offset Page 0 Page 1 Page 2 Page Number Page N-1 Program Memory/ EEPROM Memory 186 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 23. Electrical Characteristics 23.1 Absolute Maximum Ratings* *NOTICE: Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or other conditions beyond those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Operating Temperature.................................. -55C to +125C Storage Temperature ..................................... -65C to +150C Voltage on any Pin except RESET with respect to Ground ................................-0.5V to VCC+0.5V Voltage on RESET with respect to Ground......-0.5V to +13.0V Maximum Operating Voltage ............................................ 6.0V DC Current per I/O Pin ............................................... 40.0 mA DC Current VCC and GND Pins................................ 200.0 mA Injection Current at VCC=0V ................................... 5.0 mA(1) Injection Current at VCC=5V ...................................... 1.0 mA Notes: 1. Maximum current per port = 30mA 23.2 DC Characteristics TA = -40C to 125C, VCC = 2.7V to 5.5V (unless otherwise noted)(1) Symbol VIL VIH VIL1 VIH1 VIL2 VIH2 VIL3 VIH3 VOL VOH IIL IIH RRST RPU Parameter Input Low-voltage Input High-voltage Input Low-voltage Input High-voltage Input Low-voltage Input High-voltage Input Low-voltage Input High-voltage Output Low Voltage(4) (Except Reset pin) Output High-voltage(5) (Except Reset pin) Input Leakage Current I/O Pin Input Leakage Current I/O Pin Reset Pull-up Resistor I/O Pin Pull-up Resistor Condition Except XTAL1 and RESET pin Except XTAL1 and RESET pin XTAL1 pin, External Clock Selected XTAL1 pin, External Clock Selected RESET pin RESET pin RESET pin as I/O RESET pin as I/O IOL = 10 mA, VCC = 5V IOL = 5 mA, VCC = 3V IOH = -10 mA, VCC = 5V IOH = -5 mA, VCC = 3V Vcc = 5.5V, pin low (absolute value) Vcc = 5.5V, pin high (absolute value) 30 20 4.3 2.5 250 250 60 50 Min. -0.5 0.7VCC(3) -0.5 0.8VCC(3) -0.5 0.9VCC -0.5 0.7VCC (3) (3) Typ. Max. 0.2VCC VCC +0.5 0.1VCC VCC +0.5 0.2VCC VCC +0.5 0.2VCC VCC +0.5 0.6 0.5 Units V V V V V V V V V V V V nA nA k k 187 7753C-AVR-07/09 TA = -40C to 125C, VCC = 2.7V to 5.5V (unless otherwise noted)(1) (Continued) Symbol Parameter Condition Active 4MHz, VCC = 3V(6) ATD On Active 8MHz, VCC = 5V Power Supply Current ICC Idle 4MHz, VCC = 3V(6) Idle 8MHz, VCC = 5V(6) Idle 16MHz, VCC = 5V (6) (6) Min. ATD On Typ. 1.45 3.96 7.16 0.25 0.96 1.91 4 0.12 6 0.13 10 Max. 2 6 10 0.4 1.2 2.5 50 30 75 45 40 50 Units mA mA mA mA mA mA A A A A mV nA Active 16MHz, VCC = 5V(6) ATD On WDT enabled, VCC = 3V(7) Power-down mode WDT disabled, VCC = 3V WDT disabled, VCC = 5V VACIO IACLK Analog Comparator Input Offset Voltage Analog Comparator Input Leakage Current (7) WDT enabled, VCC = 5V(7) (7) VCC = 5V, Vin = VCC/2 VCC = 5V, Vin = VCC/2 -50 Notes: 1. All DC Characteristics contained in this data sheet are based on simulation and characterization of ATtiny261/461/861 AVR microcontrollers manufactured in a typical process technology. These values are preliminary values representing design targets, and will be updated after characterization of actual Automotive silicon. 2. "Max" means the highest value where the pin is guaranteed to be read as low. 3. "Min" means the lowest value where the pin is guaranteed to be read as high. 4. Although each I/O port can sink more than the test conditions (10 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state conditions (non-transient), the following must be observed: 1] The sum of all IOL, for all ports, should not exceed 60 mA. If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater than the listed test condition. 5. Although each I/O port can source more than the test conditions (10 mA at VCC = 5V, 5 mA at VCC = 3V) under steady state conditions (non-transient), the following must be observed: 1] The sum of all IOH, for all ports, should not exceed 60 mA. If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current greater than the listed test condition. 6. Values using methods described in "Minimizing Power Consumption" on page 36. Power Reduction is enabled (PRR = 0xFF) and there is no I/O drive. 7. BOD Disabled. 188 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 23.3 Speed Grades Figure 23-1. Maximum Frequency vs. VCC 16 MHz 8 MHz Safe Operating Area 2.7V 4.5V 5.5V 23.4 23.4.1 Clock Characteristics Calibrated Internal RC Oscillator Accuracy Calibration Accuracy of Internal RC Oscillator Frequency VCC 3V 8.0 MHz 2.7V to 5.5V (1) Table 23-1. Temperature 25C -40C to +125C Calibration Accuracy 2% 14% Factory Calibration Notes: 1. Voltage range for ATtiny261/461/861. 23.4.2 External Clock Drive Waveforms Figure 23-2. External Clock Drive Waveforms V IH1 V IL1 189 7753C-AVR-07/09 23.4.3 External Clock Drive External Clock Drive VCC = 2.7 - 5.5V VCC = 4.5 - 5.5V Min. 0 62.5 20 20 1.6 1.6 2 0.5 0.5 2 Max. 16 Units MHz ns ns ns s s % Parameter Clock Frequency Clock Period High Time Low Time Rise Time Fall Time Change in period from one clock cycle to the next Min. 0 125 40 40 Max. 8 Table 23-2. Symbol 1/tCLCL tCLCL tCHCX tCLCX tCLCH tCHCL tCLCL 23.5 System and Reset Characteristics Table 23-3. Symbol tRST VHYST tBOD VBG tBG IBG Notes: Reset, Brown-out and Internal Voltage Characteristics(1) Parameter Minimum pulse width on RESET Pin Brown-out Detector Hysteresis Min Pulse Width on Brown-out Reset Bandgap reference voltage Bandgap reference start-up time Bandgap reference current consumption VCC = 3.0V, TA = 25C VCC = 2.7V, TA = 25C VCC = 2.7V, TA = 25C 1.0 Condition VCC = 3V 50 2 1.1 40 15 1.2 70 Min Typ Max 2.5 Units s mV s V s A 1. Values are guidelines only. Table 23-4. BODLEVEL Fuse Coding(1) Min VBOT 1.68 2.5 4.0 Typ VBOT 1.8 2.7 4.3 Max VBOT 1.92 2.9 4.6 V Units 111 110 101 100 011 010 001 000 Reserved BOD Disabled BODLEVEL [2..0] Fuses Note: 1. VBOT may be below nominal minimum operating voltage for some devices. For devices where this is the case, the device is tested down to VCC = VBOT during the production test. This guarantees that a Brown-out Reset will occur before VCC drops to a voltage where correct operation of the microcontroller is no longer guaranteed. 190 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 23.6 ADC Characteristics ADC Characteristics, Single Ended Channels, -40C +125C Condition Single Ended Conversion VCC = 4V, VREF = 4V, ADC clock = 200 kHz VCC = 4V,VREF = 4V, ADC clock = 200 kHz VCC = 4V, VREF = 4V, ADC clock = 200 kHz VCC = 4V, VREF = 4V, ADC clock = 200 kHz VCC = 4V, VREF = 4V, ADC clock = 200 kHz -5.0 -3.5 2.56 50 VCC - 0.3 1.0 21 After Firmware Calibration Internal VREF VCC = 3V 1.1 100 30 10 39 Min Typ 10 2.0 0.6 0.2 -2.0 1.2 4.0 1.8 0.6 3.0 3.5 AVCC 200 VCC + 0.3 1.2 Max Units Bits LSB LSB LSB LSB LSB V kHz V V M k C Table 23-5. Symbol Parameter Resolution TUE INL DNL Absolute accuracy Integral Non-linearity Differential Non-linearity (DNL) Gain Error Offset Error VREF AVCC VINT RAIN RRef External Reference Voltage Clock Frequency Analog Supply Frequency Internal Voltage Reference Analog Input Resistance Reference Input Resistance Temperature Sensor Accuracy 191 7753C-AVR-07/09 Table 23-6. Symbol ADC Characteristics, Differential Channels, -40C +125C Condition Differential conversion, gain = 1x or 8x Differential conversion, gain = 20x or 32x Gain = 1x / 8x, BIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 20x / 32x, BIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 1x / 8x, UNIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 20x / 32x, UNIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 1x / 8x, BIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 20x / 32x, BIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 1x / 8x, UNIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 20x / 32x, UNIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 1x / 8x, BIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 20x / 32x, BIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 1x / 8x, UNIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 20x / 32x, UNIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Min Typ 8 Bits 8 1.7 4.0 Max Units Parameter Resolution 2.0 5.0 LSB TUE Absolute accuracy 2.3 5.0 3.0 6.0 0.3 1.5 0.7 3.0 LSB INL Integral Non-linearity 1.0 3.0 2.0 6.0 0.3 1.0 0.4 1.2 LSB DNL Differential Non-linearity 0.4 1.0 0.8 2.5 192 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Table 23-6. Symbol ADC Characteristics, Differential Channels, -40C +125C (Continued) Condition Gain = 1x / 8x, BIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 20x / 32x, BIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 1x / 8x, UNIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Gain = 20x / 32x, UNIPOLAR, VCC = 5V, VREF = 4V, ADC clock = 200 kHz Min -4.0 Typ 2.0 Max 4.0 Units Parameter -4.0 1.4 4.0 LSB Gain error -5.0 -2.6 5.0 -5.0 -0.8 5.0 Offset error Gain = 1x, VCC = 5V, VREF = 4V, ADC clock = 200 kHz -3.0 0.6 3.0 LSB VREF External Reference voltage 2.56 AVCC-0.5 V 193 7753C-AVR-07/09 23.7 Parallel Programming Characteristics Figure 23-3. Parallel Programming Timing, Including some General Timing Requirements tXLWL XTAL1 tDVXH Data & Contol (DATA, XA0, XA1/BS2, PAGEL/BS1) tBVPH tPLBX t BVWL tWLWH WR RDY/BSY tWLRH tPLWL WLRL tXHXL tXLDX tWLBX Figure 23-4. Parallel Programming Timing, Loading Sequence with Timing Requirements(1) LOAD ADDRESS (LOW BYTE) LOAD DATA (LOW BYTE) t XLXH LOAD DATA (HIGH BYTE) LOAD ADDRESS (LOW BYTE) XTAL1 PAGEL/BS1 DATA ADDR0 (Low Byte) DATA (Low Byte) DATA (High Byte) ADDR1 (Low Byte) XA0 XA1/BS2 Note: 1. The timing requirements shown in Figure 23-3 (i.e., tDVXH, tXHXL, and tXLDX) also apply to loading operation. 194 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 23-5. Parallel Programming Timing, Reading Sequence (within the Same Page) with Timing Requirements(1) LOAD ADDRESS (LOW BYTE) tXLOL READ DATA (LOW BYTE) READ DATA (HIGH BYTE) LOAD ADDRESS (LOW BYTE) XTAL1 tBVDV PAGEL/BS1 tOLDV OE tOHDZ DATA ADDR0 (Low Byte) DATA (Low Byte) DATA (High Byte) ADDR1 (Low Byte) XA0 XA1/BS2 Note: 1. The timing requirements shown in Figure 23-3 (i.e., tDVXH, tXHXL, and tXLDX) also apply to reading operation. Table 23-7. Symbol VPP IPP tDVXH tXLXH tXHXL tXLDX tXLWL tBVPH tPHPL tPLBX tWLBX tPLWL tBVWL tWLWH tWLRL tWLRH tWLRH_CE tXLOL tBVDV tOLDV tOHDZ Notes: 1. Parallel Programming Characteristics, VCC = 5V 10% Parameter Programming Enable Voltage Programming Enable Current Data and Control Valid before XTAL1 High XTAL1 Low to XTAL1 High XTAL1 Pulse Width High Data and Control Hold after XTAL1 Low XTAL1 Low to WR Low BS1 Valid before PAGEL High PAGEL Pulse Width High BS1 Hold after PAGEL Low BS2/1 Hold after WR Low PAGEL Low to WR Low BS1 Valid to WR Low WR Pulse Width Low WR Low to RDY/BSY Low WR Low to RDY/BSY High(1) WR Low to RDY/BSY High for Chip Erase(2) XTAL1 Low to OE Low BS1 Valid to DATA valid OE Low to DATA Valid OE High to DATA Tri-stated 67 200 150 67 0 67 150 67 67 67 67 150 0 3.7 7.5 0 0 250 250 250 1 4.5 9 Min 11.5 Typ Max 12.5 250 Units V A ns ns ns ns ns ns ns ns ns ns ns ns s ms ms ns ns ns ns tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock bits commands. 2. tWLRH_CE is valid for the Chip Erase command. 195 7753C-AVR-07/09 23.8 Serial Programming Characteristics Figure 23-6. Serial Programming Waveforms SERIAL DATA INPUT (MOSI) SERIAL DATA OUTPUT (MISO) SERIAL CLOCK INPUT (SCK) SAMPLE MSB LSB MSB LSB Figure 23-7. Serial Programming Timing MOSI tOVSH SCK MISO tSLIV tSHSL tSHOX tSLSH Table 23-8. Symbol 1/tCLCL tCLCL 1/tCLCL tCLCL 1/tCLCL tCLCL tSHSL tSLSH tOVSH tSHOX tSLIV Note: Serial Programming Characteristics, TA = -40C to 125C, VCC = 2.7 - 5.5V (Unless Otherwise Noted) Parameter Oscillator Frequency (ATtiny261/461/861V) Oscillator Period (ATtiny261/461/861V) Oscillator Frequency (ATtiny261/461/861L, VCC = 2.7 - 5.5V) Oscillator Period (ATtiny261/461/861L, VCC = 2.7 5.5V) Oscillator Frequency (ATtiny261/461/861, VCC = 4.5V - 5.5V) Oscillator Period (ATtiny261/461/861, VCC = 4.5V 5.5V) SCK Pulse Width High SCK Pulse Width Low MOSI Setup to SCK High MOSI Hold after SCK High SCK Low to MISO Valid Min 0 250 0 100 0 50 2 tCLCL* 2 tCLCL* tCLCL 2 tCLCL TBD TBD TBD 16 10 Typ Max 4 Units MHz ns MHz ns MHz ns ns ns ns ns ns 1. 2 tCLCL for fck < 12 MHz, 3 tCLCL for fck >= 12 MHz 196 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 24. Typical Characteristics The data contained in this section is largely based on simulations and characterization of similar devices in the same process and design methods. These values are preliminary values representing design targets, and will be updated after characterization of actual Automotive silicon. Thus, the data should be treated as indications of how the part will behave. The following charts show typical behavior. These figures are not tested during manufacturing. All current consumption measurements are performed with all I/O pins configured as inputs and with internal pull-ups enabled. A sine wave generator with rail-to-rail output is used as clock source. The power consumption in Power-down mode is independent of clock selection. The current consumption is a function of several factors such as: operating voltage, operating frequency, loading of I/O pins, switching rate of I/O pins, code executed and ambient temperature. The dominating factors are operating voltage and frequency. The current drawn from capacitive loaded pins may be estimated (for one pin) as CL*VCC*f where CL = load capacitance, VCC = operating voltage and f = average switching frequency of I/O pin. The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to function properly at frequencies higher than the ordering code indicates. The difference between current consumption in Power-down mode with Watchdog Timer enabled and Power-down mode with Watchdog Timer disabled represents the differential current drawn by the Watchdog Timer. Unless otherwise specified the data contained in this chapter are for -40C to +85C. 24.1 Active Supply Current Figure 24-1. Active Supply Current vs. Low Frequency (0.1 - 1.0 MHz) 197 7753C-AVR-07/09 Figure 24-2. Active Supply Current vs. Frequency (1 - 16 MHz) 24.2 Idle Supply Current Figure 24-3. Idle Supply Current vs. Frequency (1 - 16 MHz) 198 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 24.3 Supply Current of I/O modules The tables and formulas below can be used to calculate the additional current consumption for the different I/O modules in Active and Idle mode. The enabling or disabling of the I/O modules are controlled by the Power Reduction Register. See "PRR - Power Reduction Register" on page 38 for details. Table 24-1. PRR bit Additional Current Consumption for the different I/O modules (absolute values) Typical numbers VCC = 2V, F = 1MHz VCC = 3V, F = 4MHz 423 uA 39 uA 25 uA 111 uA VCC = 5V, F = 8MHz 1787 uA 165 uA 457 uA 102 uA PRTIM1 PRTIM0 PRUSI PRADC 65 uA 7 uA 5 uA 18 uA Table 24-2. Additional Current Consumption (percentage) in Active and Idle mode Additional Current consumption compared to Active with external clock (see Figure 24-1 on page 197 and Figure 24-2 on page 198) 26.9% 2.6% 1.7% 7.1% PRR bit PRTIM1 PRTIM0 PRUSI PRADC Additional Current consumption compared to Idle with external clock 103.7% 10.0% 6.5% 27.3% It is possible to calculate the typical current consumption based on the numbers from Table 24-1 for other VCC and frequency settings than listed in Table 24-2. 24.3.1 Example Calculate the expected current consumption in idle mode with TIMER0, ADC, and USI enabled at VCC = 2.0V and F = 1MHz. From Table 24-2, third column, we see that we need to add 10% for the TIMER0, 27.3% for the ADC, and 6.5% for the USI module. Reading from Figure 24-3 on page 198, we find that the idle current consumption is ~0,085 mA at VCC = 2.0V and F=1MHz. The total current consumption in idle mode with TIMER0, ADC, and USI enabled, gives: ICCtotal 0,085mA * ( 1 + 0,10 + 0,273 + 0,065 ) 0,122mA 199 7753C-AVR-07/09 24.4 Power-down Supply Current Figure 24-4. Power-down Supply Current vs. VCC (Watchdog Timer Disabled) Figure 24-5. Power-down Supply Current vs. VCC (Watchdog Timer Enabled) 200 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 24.5 Pin Pull-up Figure 24-6. I/O Pin pull-up Resistor Current vs. Input Voltage (VCC = 5V) Figure 24-7. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 5V) 201 7753C-AVR-07/09 24.6 Pin Driver Strength Figure 24-8. I/O Pin Output Voltage vs. Sink Current (VCC = 3V) Figure 24-9. I/O Pin Output Voltage vs. Sink Current (VCC = 5V) 202 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 24-10. I/O Pin Output Voltage vs. Source Current (VCC = 3V) Figure 24-11. I/O Pin Output Voltage vs. Source Current (VCC = 5V) 203 7753C-AVR-07/09 24.7 Pin Threshold and Hysteresis Figure 24-12. I/O Pin Input Threshold Voltage vs. VCC (VIH, I/O Pin Read as `1') Figure 24-13. I/O Pin Input Threshold Voltage vs. VCC (VIL, I/O Pin Read as `0') 204 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 24-14. Reset Input Threshold Voltage vs. VCC (VIH, Reset Read as `1') Figure 24-15. Reset Input Threshold Voltage vs. VCC (VIL, Reset Read as `0') 205 7753C-AVR-07/09 24.8 BOD Threshold and Analog Comparator Offset Figure 24-16. BOD Threshold vs. Temperature (BOD Level is 4.3V) Figure 24-17. BOD Threshold vs. Temperature (BOD Level is 2.7V) 206 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 Figure 24-18. BOD Threshold vs. Temperature (BOD Level is 1.8V) 24.9 Internal Oscillator Speed Figure 24-19. Watchdog Oscillator Frequency vs. Temperature 207 7753C-AVR-07/09 Figure 24-20. Calibrated 8.0 MHz RC Oscillator Frequency vs. Temperature 208 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 25. Register Summary Address 0x3F (0x5F) 0x3E (0x5E) 0x3D (0x5D) 0x3C (0x5C) 0x3B (0x5B) 0x3A (0x5A) 0x39 (0x59) 0x38 (0x58) 0x37 (0x57) 0x36 (0x56) 0x35 (0x55) 0x34 (0x54) 0x33 (0x53) 0x32 (0x52) 0x31 (0x51) 0x30 (0x50) 0x2F (0x4F) 0x2E (0x4E) 0x2D (0x4D) 0x2C (0x4C) 0x2B (0x4B) 0x2A (0x4A) 0x29 (0x49) 0x28 (0x48) 0x27 (0x47) 0x26 (0x46) 0x25 (0x45) 0x24 (0x44) 0x23 (0x43) 0x22 (0x42) 0x21 (0x41) 0x20 (0x40) 0x1F (0x3F) 0x1E (0x3E) 0x1D (0x3D) 0x1C (0x3C) 0x1B (0x3B) 0x1A (0x3A) 0x19 (0x39) 0x18 (0x38) 0x17 (0x37) 0x16 (0x36) 0x15 (0x35) 0x14 (0x34) 0x13 (0x33) 0x12 (0x32) 0x11 (0x31) 0x10 (0x30) 0x0F (0x2F) 0x0E (0x2E) 0x0D (0x2D) 0x0C (0x2C) 0x0B (0x2B) 0x0A (0x2A) Name SREG SPH SPL Reserved GIMSK GIFR TIMSK TIFR SPMCSR PRR MCUCR MCUSR TCCR0B TCNT0L OSCCAL TCCR1A TCCR1B TCNT1 OCR1A OCR1B OCR1C OCR1D PLLCSR CLKPR TCCR1C TCCR1D TC1H DT1 PCMSK0 PCMSK1 WDTCR DWDR EEARH EEARL EEDR EECR PORTA DDRA PINA PORTB DDRB PINB TCCR0A TCNT0H OCR0A OCR0B USIPP USIBR USIDR USISR USICR GPIOR2 GPIOR1 GPIOR0 Bit 7 I - SP7 INT1 INTF1 OCIE1D OCF1D - - - - Bit 6 T - SP6 INT0 INTF0 OCIE1A OCF1A - PUD - - Bit 5 H - SP5 PCIE1 PCIF OCIE1B OCF1B SIGRD SE - - Bit 4 S - SP4 - PCIE0 - OCIE0A OCF0A CTPB SM1 - TSM Bit 3 V - SP3 - - OCIE0B OCF0B RFLB PRTIM1 SM0 WDRF PSR0 Bit 2 N SP10 SP2 - - TOIE1 TOV1 PGWRT PRTIM0 - BORF CS02 Bit 1 Z SP9 SP1 - - TOIE0 TOV0 PGERS PRUSI ISC01 EXTRF CS01 Bit 0 C SP8 SP0 - - TICIE0 ICF0 SPMEN PRADC ISC00 PORF CS00 Page page 11 page 13 page 13 page 53 page 53 page 87, page 125 page 88, page 126 page 169 page 36 page 38, page 69, page 52 page 45, page 71 page 86 page 32 Timer/Counter0 Counter Register Low Byte Oscillator Calibration Register COM1A1 PWM1X COM1A0 PSR1 COM1B1 DTPS11 COM1B0 DTPS10 FOC1A CS13 FOC1B CS12 PWM1A CS11 PWM1B CS10 page 115 page 169 page 123 page 124 page 124 page 124 page 125 Timer/Counter1 Counter Register Timer/Counter1 Output Compare Register A Timer/Counter1 Output Compare Register B Timer/Counter1 Output Compare Register C Timer/Counter1 Output Compare Register D LSM CLKPCE COM1A1S FPIE1 DT1H3 PCINT7 PCINT15 WDIF COM1A0S FPEN1 DT1H2 PCINT6 PCINT14 WDIE COM1B1S FPNC1 DT1H1 PCINT5 PCINT13 WDP3 COM1B0S FPES1 DT1H0 PCINT4 PCINT12 WDCE CLKPS3 COM1D1 FPAC1 DT1L3 PCINT3 PCINT11 WDE PCKE CLKPS2 COM1D0 FPF1 DT1L2 PCINT2 PCINT10 WDP2 PLLE CLKPS1 FOC1D WGM11 TC19 DT1L1 PCINT1 PCINT9 WDP1 PLOCK CLKPS0 PWM1D WGM10 TC18 DT1L0 PCINT0 PCINT8 WDP0 EEAR8 EEAR7 - PORTA7 DDA7 PINA7 PORTB7 DDB7 PINB7 TCW0 EEAR6 - PORTA6 DDA6 PINA6 PORTB6 DDB6 PINB6 ICEN0 EEAR5 EEPM1 PORTA5 DDA5 PINA5 PORTB5 DDB5 PINB5 ICNC0 EEAR4 EEPM0 PORTA4 DDA4 PINA4 PORTB4 DDB4 PINB4 ICES0 EEAR3 EERIE PORTA3 DDA3 PINA3 PORTB3 DDB3 PINB3 ACIC0 EEAR2 EEMPE PORTA2 DDA2 PINA2 PORTB2 DDB2 PINB2 EEAR1 EEPE PORTA1 DDA1 PINA1 PORTB1 DDB1 PINB1 EEAR0 EERE PORTA0 DDA0 PINA0 PORTB0 DDB0 PINB0 CTC0 EEPROM Data Register page 90 page 33 page 119 page 121 page 123 page 127 page 54 page 54 page 46 page 36 page 22 page 22 page 23 page 23 page 69 page 69 page 69 page 69 page 69 page 69 page 85 page 86 page 86 page 86 DWDR[7:0] Timer/Counter0 Counter Register High Byte Timer/Counter0 Output Compare Register A Timer/Counter0 Output Compare Register B USIPOS USI Buffer Register USI Data Register USISIF USISIE USIOIF USIOIE USIPF USIWM1 USIDC USIWM0 USICNT3 USICS1 USICNT2 USICS0 USICNT1 USICLK USICNT0 USITC page 139 page 136 page 135 page 136 page 137 page 24 page 24 page 24 General Purpose I/O Register 2 General Purpose I/O Register 1 General Purpose I/O Register 0 Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses should never be written. 2. I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the value of single bits can be checked by using the SBIS and SBIC instructions. 3. Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI instructions will only operation the specified bit, and can therefore be used on registers containing such Status Flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only. 209 7753C-AVR-07/09 25. Register Summary (Continued) Address 0x09 (0x29) 0x08 (0x28) 0x07 (0x27) 0x06 (0x26) 0x05 (0x25) 0x04 (0x24) 0x03 (0x23) 0x02 (0x22) 0x01 (0x21) 0x00 (0x20) Name ACSRB ACSRA ADMUX ADCSRA ADCH ADCL ADCSRB DIDR1 DIDR0 TCCR1E Bit 7 HSEL ACD REFS1 ADEN Bit 6 HLEV ACBG REFS0 ADSC Bit 5 ACO ADLAR ADATE Bit 4 ACI MUX4 ADIF Bit 3 ACIE MUX3 ADIE Bit 2 ACM2 ACME MUX2 ADPS2 Bit 1 ACM1 ACIS1 MUX1 ADPS1 Bit 0 ACM0 ACIS0 MUX0 ADPS0 Page page 143 page 140 page 157 page 160 page 161 page 161 ADC Data Register High Byte ADC Data Register Low Byte BIN ADC10D ADC6D - GSEL ADC9D ADC5D ADC8D ADC4D OC1OE5 REFS2 ADC7D ADC3D OC1OE4 AREFD OC1OE3 ADC2D OC1OE2 ADC1D OC1OE1 ADC0D OC1OE0 MUX5 ADTS2 ADTS1 ADTS0 page 162 page 163 page 163 page 122 Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses should never be written. 2. I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the value of single bits can be checked by using the SBIS and SBIC instructions. 3. Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI instructions will only operation the specified bit, and can therefore be used on registers containing such Status Flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only. 210 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 26. Instruction Set Summary Mnemonics ADD ADC ADIW SUB SUBI SBC SBCI SBIW AND ANDI OR ORI EOR COM NEG SBR CBR INC DEC TST CLR SER RJMP IJMP RCALL ICALL RET RETI CPSE CP CPC CPI SBRC SBRS SBIC SBIS BRBS BRBC BREQ BRNE BRCS BRCC BRSH BRLO BRMI BRPL BRGE BRLT BRHS BRHC BRTS BRTC BRVS BRVC BRIE BRID SBI CBI LSL LSR Rd,Rr Rd,Rr Rd,Rr Rd,K Rr, b Rr, b P, b P, b s, k s, k k k k k k k k k k k k k k k k k k k P,b P,b Rd Rd k Operands Rd, Rr Rd, Rr Rdl,K Rd, Rr Rd, K Rd, Rr Rd, K Rdl,K Rd, Rr Rd, K Rd, Rr Rd, K Rd, Rr Rd Rd Rd,K Rd,K Rd Rd Rd Rd Rd k Add two Registers Description Rd Rd + Rr Rd Rd + Rr + C Operation Flags Z,C,N,V,H Z,C,N,V,H Z,C,N,V,S Z,C,N,V,H Z,C,N,V,H Z,C,N,V,H Z,C,N,V,H Z,C,N,V,S Z,N,V Z,N,V Z,N,V Z,N,V Z,N,V Z,C,N,V Z,C,N,V,H Z,N,V Z,N,V Z,N,V Z,N,V Z,N,V Z,N,V None None None None None None I None Z, N,V,C,H Z, N,V,C,H Z, N,V,C,H None None None None None None None None None None None None None None None None None None None None None None None None None None Z,C,N,V Z,C,N,V #Clocks 1 1 2 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 3 3 4 4 1/2/3 1 1 1 1/2/3 1/2/3 1/2/3 1/2/3 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 2 2 1 1 ARITHMETIC AND LOGIC INSTRUCTIONS Add with Carry two Registers Add Immediate to Word Subtract two Registers Subtract Constant from Register Subtract with Carry two Registers Subtract with Carry Constant from Reg. Subtract Immediate from Word Logical AND Registers Logical AND Register and Constant Logical OR Registers Logical OR Register and Constant Exclusive OR Registers One's Complement Two's Complement Set Bit(s) in Register Clear Bit(s) in Register Increment Decrement Test for Zero or Minus Clear Register Set Register Relative Jump Indirect Jump to (Z) Relative Subroutine Call Indirect Call to (Z) Subroutine Return Interrupt Return Compare, Skip if Equal Compare Compare with Carry Compare Register with Immediate Skip if Bit in Register Cleared Skip if Bit in Register is Set Skip if Bit in I/O Register Cleared Skip if Bit in I/O Register is Set Branch if Status Flag Set Branch if Status Flag Cleared Branch if Equal Branch if Not Equal Branch if Carry Set Branch if Carry Cleared Branch if Same or Higher Branch if Lower Branch if Minus Branch if Plus Branch if Greater or Equal, Signed Branch if Less Than Zero, Signed Branch if Half Carry Flag Set Branch if Half Carry Flag Cleared Branch if T Flag Set Branch if T Flag Cleared Branch if Overflow Flag is Set Branch if Overflow Flag is Cleared Branch if Interrupt Enabled Branch if Interrupt Disabled Set Bit in I/O Register Clear Bit in I/O Register Logical Shift Left Logical Shift Right Rdh:Rdl Rdh:Rdl + K Rd Rd - Rr Rd Rd - K Rd Rd - Rr - C Rd Rd - K - C Rdh:Rdl Rdh:Rdl - K Rd Rd * Rr Rd Rd * K Rd Rd v Rr Rd Rd v K Rd Rd Rr Rd 0xFF -Rd Rd 0x00 -Rd Rd Rd v K Rd Rd * (0xFF - K) Rd Rd + 1 Rd Rd -1 Rd Rd * Rd Rd Rd Rd Rd 0xFF PC PC + k + 1 PC Z PC PC + k + 1 PC Z PC STACK PC STACK if (Rd = Rr) PC PC + 2 or 3 Rd -Rr Rd -Rr -C Rd -K if (Rr(b)=0) PC PC + 2 or 3 if (Rr(b)=1) PC PC + 2 or 3 if (P(b)=0) PC PC + 2 or 3 if (P(b)=1) PC PC + 2 or 3 if (SREG(s) = 1) then PC PC+k + 1 if (SREG(s) = 0) then PC PC+k + 1 if (Z = 1) then PC PC + k + 1 if (Z = 0) then PC PC + k + 1 if (C = 1) then PC PC + k + 1 if (C = 0) then PC PC + k + 1 if (C = 0) then PC PC + k + 1 if (C = 1) then PC PC + k + 1 if (N = 1) then PC PC + k + 1 if (N = 0) then PC PC + k + 1 if (N V= 0) then PC PC + k + 1 if (N V= 1) then PC PC + k + 1 if (H = 1) then PC PC + k + 1 if (H = 0) then PC PC + k + 1 if (T = 1) then PC PC + k + 1 if (T = 0) then PC PC + k + 1 if (V = 1) then PC PC + k + 1 if (V = 0) then PC PC + k + 1 if ( I = 1) then PC PC + k + 1 if ( I = 0) then PC PC + k + 1 I/O(P,b) 1 I/O(P,b) 0 Rd(n+1) Rd(n), Rd(0) 0 Rd(n) Rd(n+1), Rd(7) 0 BRANCH INSTRUCTIONS BIT AND BIT-TEST INSTRUCTIONS 211 7753C-AVR-07/09 26. Instruction Set Summary (Continued) Mnemonics ROL ROR ASR SWAP BSET BCLR BST BLD SEC CLC SEN CLN SEZ CLZ SEI CLI SES CLS SEV CLV SET CLT SEH CLH DATA TRANSFER INSTRUCTIONS MOV MOVW LDI LD LD LD LD LD LD LDD LD LD LD LDD LDS ST ST ST ST ST ST STD ST ST ST STD STS LPM LPM LPM SPM IN OUT PUSH POP NOP SLEEP WDR BREAK Rd, P P, Rr Rr Rd Rd, Z Rd, Z+ Rd, Rr Rd, Rr Rd, K Rd, X Rd, X+ Rd, - X Rd, Y Rd, Y+ Rd, - Y Rd,Y+q Rd, Z Rd, Z+ Rd, -Z Rd, Z+q Rd, k X, Rr X+, Rr - X, Rr Y, Rr Y+, Rr - Y, Rr Y+q,Rr Z, Rr Z+, Rr -Z, Rr Z+q,Rr k, Rr Move Between Registers Copy Register Word Load Immediate Load Indirect Load Indirect and Post-Inc. Load Indirect and Pre-Dec. Load Indirect Load Indirect and Post-Inc. Load Indirect and Pre-Dec. Load Indirect with Displacement Load Indirect Load Indirect and Post-Inc. Load Indirect and Pre-Dec. Load Indirect with Displacement Load Direct from SRAM Store Indirect Store Indirect and Post-Inc. Store Indirect and Pre-Dec. Store Indirect Store Indirect and Post-Inc. Store Indirect and Pre-Dec. Store Indirect with Displacement Store Indirect Store Indirect and Post-Inc. Store Indirect and Pre-Dec. Store Indirect with Displacement Store Direct to SRAM Load Program Memory Load Program Memory Load Program Memory and Post-Inc Store Program Memory In Port Out Port Push Register on Stack Pop Register from Stack No Operation Sleep Watchdog Reset Break (see specific descr. for Sleep function) (see specific descr. for WDR/Timer) For On-chip Debug Only Rd Rr Rd+1:Rd Rr+1:Rr Rd K Rd (X) Rd (X), X X + 1 X X - 1, Rd (X) Rd (Y) Rd (Y), Y Y + 1 Y Y - 1, Rd (Y) Rd (Y + q) Rd (Z) Rd (Z), Z Z+1 Z Z - 1, Rd (Z) Rd (Z + q) Rd (k) (X) Rr (X) Rr, X X + 1 X X - 1, (X) Rr (Y) Rr (Y) Rr, Y Y + 1 Y Y - 1, (Y) Rr (Y + q) Rr (Z) Rr (Z) Rr, Z Z + 1 Z Z - 1, (Z) Rr (Z + q) Rr (k) Rr R0 (Z) Rd (Z) Rd (Z), Z Z+1 (z) R1:R0 Rd P P Rr STACK Rr Rd STACK None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None 1 1 2 2 1 1 1 N/A 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 Rd Rd Rd Rd s s Rr, b Rd, b Operands Description Rotate Left Through Carry Rotate Right Through Carry Arithmetic Shift Right Swap Nibbles Flag Set Flag Clear Bit Store from Register to T Bit load from T to Register Set Carry Clear Carry Set Negative Flag Clear Negative Flag Set Zero Flag Clear Zero Flag Global Interrupt Enable Global Interrupt Disable Set Signed Test Flag Clear Signed Test Flag Set Twos Complement Overflow. Clear Twos Complement Overflow Set T in SREG Clear T in SREG Set Half Carry Flag in SREG Clear Half Carry Flag in SREG Operation Rd(0) C,Rd(n+1)Rd(n),C Rd(7) Rd(7) C,Rd(n)Rd(n+1),C Rd(0) Rd(n) Rd(n+1), n=0..6 Rd(3..0) Rd(7..4),Rd(7..4) Rd(3..0) SREG(s) 1 SREG(s) 0 T Rr(b) Rd(b) T C 1 C 0 N 1 N 0 Z 1 Z 0 I 1 I 0 S 1 S 0 V 1 V 0 T 1 T 0 H 1 H 0 Flags Z,C,N,V Z,C,N,V Z,C,N,V None SREG(s) SREG(s) T None C C N N Z Z I I S S V V T T H H #Clocks 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 MCU CONTROL INSTRUCTIONS 212 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 27. Ordering Information Table 27-1. Engineering Samples Delivery only Speed (MHz)(3) 16 16 16 16 16 16 16 16 16 Power Supply (V) 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 Package(1) TG PN 6G TG PN 6G TG PN 6G Operation Range Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Ordering Code(2) ATtiny261-ESSZ ATtiny261-ESMZ ATtiny261-ESXZ ATtiny461-ESSZ ATtiny461-ESMZ ATtiny461-ESXZ ATtiny861-ESSZ ATtiny861-ESMZ ATtiny861-ESXZ Table 27-2. Available Product Offering Speed (MHz)(3) 16 16 16 16 16 16 16 16 16 16 16 16 Power Supply (V) 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 2.7 - 5.5 Package(1) TG PN 6G PC TG PN 6G PC TG PN 6G PC Operation Range Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Automotive (-40 to +125C) Ordering Code(2) ATtiny261-15SZ ATtiny261-15MZ ATtiny261-15XZ ATtiny261-15MAZ ATtiny461-15SZ ATtiny461-15MZ ATtiny461-15XZ ATtiny461-15MAZ ATtiny861-15SZ ATtiny861-15MZ ATtiny861-15XZ ATTINY861-15MAZ Notes: 1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information and minimum quantities. 2. Pb-free packaging, complies to the European Directive for Restriction of Hazardous Substances (RoHS directive). Also Halide free and fully Green. 3. For Speed vs. VCC, see Figure 23.3 on page 189. 213 7753C-AVR-07/09 Package Type PN TG 6G PC 32-pad, 5.0x5.0 mm Body, Lead Pitch 0.50 mm, Quad Flat No Lead Package (QFN) 20-lead, 0.300" Wide Body Lead, Plastic Gull Wing Small Outline Package (SOIC) 20-lead, 4.4x6.5 mm Body, 0.65 mm Pitch, Lead Length: 0.6 mm Thin Shrink Small Outline Package (TSSOP) 20-lead, 4.0x4.0 mm Body, 0.50 mm Pitch, Quad Flat No Lead Package (QFN) 214 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 28. Packaging Information 28.1 PN 215 7753C-AVR-07/09 28.2 TG 216 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 217 7753C-AVR-07/09 28.3 6G 218 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 28.4 PC 219 7753C-AVR-07/09 29. Errata 29.1 Errata ATtiny261 The revision letter in this section refers to the revision of the ATtiny261 device. 29.1.1 Rev A No known errata. 29.2 Errata ATtiny461 The revision letter in this section refers to the revision of the ATtiny461 device. 29.2.1 Rev B No known errata. 29.3 Errata ATtiny861 The revision letter in this section refers to the revision of the ATtiny861 device. 29.3.1 Rev B No known errata. 220 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 30. Revision History 30.1 7753A-AVR-11/07 * First datasheet draft - initial automotive version. Started from industrial datasheet doc2588 rev.B - 01/07 30.2 7753B-AVR-08/08 * Added 6G product offering to Ordering Information. 30.3 7753C-AVR-07/09 * QFN package added * ADC characteristics updated * Temps sensor updated * Typical characteristics updated 221 7753C-AVR-07/09 31. Table of Contents Features ..................................................................................................... 1 1 Pin Configurations ................................................................................... 2 1.1 1.2 Disclaimer ..........................................................................................................3 Automotive Quality Grade .................................................................................3 2 Overview ................................................................................................... 4 2.1 2.2 Block Diagram ...................................................................................................4 Pin Descriptions .................................................................................................5 3 4 5 Resources ................................................................................................. 7 About Code Examples ............................................................................. 8 AVR CPU Core .......................................................................................... 9 5.1 5.2 5.3 5.4 5.5 5.6 5.7 Overview ............................................................................................................9 ALU - Arithmetic Logic Unit .............................................................................10 Status Register ................................................................................................11 General Purpose Register File ........................................................................12 Stack Pointer ...................................................................................................13 Instruction Execution Timing ...........................................................................14 Reset and Interrupt Handling ...........................................................................15 6 AVR Memories ........................................................................................ 17 6.1 6.2 6.3 6.4 6.5 In-System Re-programmable Flash Program Memory ....................................17 SRAM Data Memory ........................................................................................17 EEPROM Data Memory ..................................................................................18 I/O Memory ......................................................................................................22 Register Description ........................................................................................22 7 System Clock and Clock Options ......................................................... 25 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Clock Systems and their Distribution ...............................................................25 Clock Sources .................................................................................................27 Default Clock Source .......................................................................................27 External Clock .................................................................................................27 High Frequency PLL Clock - PLLCLK .............................................................28 Calibrated Internal RC Oscillator .....................................................................29 128 kHz Internal Oscillator ..............................................................................30 Low-frequency Crystal Oscillator .....................................................................30 222 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 7.9 7.10 7.11 7.12 Crystal Oscillator .............................................................................................30 Clock Output Buffer .........................................................................................32 System Clock Prescaler ..................................................................................32 Register Description ........................................................................................32 8 Power Management and Sleep Modes ................................................. 35 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 Sleep Modes ....................................................................................................35 Idle Mode .........................................................................................................35 ADC Noise Reduction Mode ............................................................................36 Power-down Mode ...........................................................................................36 Standby Mode .................................................................................................36 Power Reduction Register ...............................................................................36 Minimizing Power Consumption ......................................................................36 Register Description ........................................................................................38 9 System Control and Reset .................................................................... 40 9.1 9.2 9.3 9.4 Internal Voltage Reference ..............................................................................44 Watchdog Timer ..............................................................................................44 Timed Sequences for Changing the Configuration of the Watchdog Timer ....45 Register Description ........................................................................................45 10 Interrupts ................................................................................................ 50 10.1 Interrupt Vectors in ATtiny261/461/861 ...........................................................50 11 External Interrupts ................................................................................. 52 11.1 Register Description ........................................................................................52 12 I/O Ports .................................................................................................. 55 12.1 12.2 12.3 12.4 Overview ..........................................................................................................55 Ports as General Digital I/O .............................................................................56 Alternate Port Functions ..................................................................................60 Register Description ........................................................................................69 13 Timer/Counter0 Prescaler ..................................................................... 70 13.1 Register Description ........................................................................................71 14 Timer/Counter0 ...................................................................................... 73 14.1 14.2 14.3 14.4 Features ..........................................................................................................73 Overview ..........................................................................................................73 Timer/Counter Clock Sources .........................................................................74 Counter Unit ....................................................................................................74 223 7753C-AVR-07/09 14.5 14.6 14.7 14.8 14.9 14.10 Modes of Operation .........................................................................................75 Input Capture Unit ...........................................................................................77 Output Compare Unit .......................................................................................78 Timer/Counter Timing Diagrams .....................................................................79 Accessing Registers in 16-bit Mode ................................................................81 Register Description ........................................................................................85 15 Timer/Counter1 Prescaler ..................................................................... 89 15.1 Register Description ........................................................................................90 16 Timer/Counter1 ...................................................................................... 92 16.1 16.2 16.3 16.4 16.5 16.6 16.7 16.8 16.9 16.10 16.11 Features ..........................................................................................................92 Overview ..........................................................................................................92 Counter Unit ....................................................................................................96 Output Compare Unit .......................................................................................97 Dead Time Generator ......................................................................................99 Compare Match Output Unit ..........................................................................100 Modes of Operation .......................................................................................102 Timer/Counter Timing Diagrams ...................................................................109 Fault Protection Unit ......................................................................................111 Accessing 10-Bit Registers ............................................................................112 Register Description ......................................................................................115 17 USI - Universal Serial Interface .......................................................... 128 17.1 17.2 17.3 17.4 17.5 Features ........................................................................................................128 Overview ........................................................................................................128 Functional Descriptions .................................................................................129 Alternative USI Usage ...................................................................................135 Register Descriptions ....................................................................................135 18 AC - Analog Comparator .................................................................... 140 18.1 18.2 Register Description ......................................................................................140 Analog Comparator Multiplexed Input ...........................................................141 19 ADC - Analog to Digital Converter ..................................................... 144 19.1 19.2 19.3 19.4 Features ........................................................................................................144 Overview ........................................................................................................144 Operation .......................................................................................................145 Starting a Conversion ....................................................................................146 224 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 ATtiny261/ATtiny461/ATtiny861 19.5 19.6 19.7 19.8 19.9 19.10 Prescaling and Conversion Timing ................................................................147 Changing Channel or Reference Selection ...................................................149 ADC Noise Canceler .....................................................................................151 ADC Conversion Result .................................................................................154 Temperature Measurement ...........................................................................155 Register Description ......................................................................................157 20 debugWIRE On-chip Debug System .................................................. 164 20.1 20.2 20.3 20.4 20.5 20.6 Features ........................................................................................................164 Overview ........................................................................................................164 Physical Interface ..........................................................................................164 Software Break Points ...................................................................................165 Limitations of debugWIRE .............................................................................165 Register Description ......................................................................................165 21 Self-Programming the Flash ............................................................... 166 21.1 21.2 21.3 21.4 21.5 Performing Page Erase by SPM ....................................................................166 Filling the Temporary Buffer (Page Loading) .................................................166 Performing a Page Write ...............................................................................167 Addressing the Flash During Self-Programming ...........................................167 Register Description ......................................................................................169 22 Memory Programming ......................................................................... 171 22.1 22.2 22.3 22.4 22.5 22.6 22.7 22.8 22.9 Program And Data Memory Lock Bits ...........................................................171 Fuse Bytes .....................................................................................................172 Signature Bytes .............................................................................................173 Calibration Byte .............................................................................................173 Reading the Signature Row from Software ...................................................174 Page Size ......................................................................................................174 Parallel Programming Parameters, Pin Mapping, and Commands ...............174 Parallel Programming ....................................................................................176 Serial Downloading ........................................................................................183 23 Electrical Characteristics .................................................................... 187 23.1 23.2 23.3 23.4 23.5 Absolute Maximum Ratings* .........................................................................187 DC Characteristics .........................................................................................187 Speed Grades ...............................................................................................189 Clock Characteristics .....................................................................................189 System and Reset Characteristics ................................................................190 225 7753C-AVR-07/09 23.6 23.7 23.8 ADC Characteristics ......................................................................................191 Parallel Programming Characteristics ...........................................................194 Serial Programming Characteristics ..............................................................196 24 Typical Characteristics ........................................................................ 197 24.1 24.2 24.3 24.4 24.5 24.6 24.7 24.8 24.9 Active Supply Current ....................................................................................197 Idle Supply Current ........................................................................................198 Supply Current of I/O modules ......................................................................199 Power-down Supply Current ..........................................................................200 Pin Pull-up .....................................................................................................201 Pin Driver Strength ........................................................................................202 Pin Threshold and Hysteresis ........................................................................204 BOD Threshold and Analog Comparator Offset ............................................206 Internal Oscillator Speed ...............................................................................207 25 Register Summary ............................................................................... 209 26 Instruction Set Summary .................................................................... 211 27 Ordering Information ........................................................................... 213 28 Packaging Information ........................................................................ 215 28.1 28.2 28.3 28.4 PN .................................................................................................................215 TG .................................................................................................................216 6G .................................................................................................................218 PC .................................................................................................................219 29 Errata ..................................................................................................... 220 29.1 29.2 29.3 Errata ATtiny261 ............................................................................................220 Errata ATtiny461 ............................................................................................220 Errata ATtiny861 ............................................................................................220 30 Revision History ................................................................................... 221 30.1 30.2 30.3 7753A-AVR-11/07 .........................................................................................221 7753B-AVR-08/08 .........................................................................................221 7753C-AVR-06/09 .........................................................................................221 31 Table of Contents ................................................................................. 222 226 ATtiny261/ATtiny461/ATtiny861 7753C-AVR-07/09 Headquarters Atmel Corporation 2325 Orchard Parkway San Jose, CA 95131 USA Tel: 1(408) 441-0311 Fax: 1(408) 487-2600 International Atmel Asia Unit 1-5 & 16, 19/F BEA Tower, Millennium City 5 418 Kwun Tong Road Kwun Tong, Kowloon Hong Kong Tel: (852) 2245-6100 Fax: (852) 2722-1369 Atmel Europe Le Krebs 8, Rue Jean-Pierre Timbaud BP 309 78054 Saint-Quentin-en-Yvelines Cedex France Tel: (33) 1-30-60-70-00 Fax: (33) 1-30-60-71-11 Atmel Japan 9F, Tonetsu Shinkawa Bldg. 1-24-8 Shinkawa Chuo-ku, Tokyo 104-0033 Japan Tel: (81) 3-3523-3551 Fax: (81) 3-3523-7581 Product Contact Web Site www.atmel.com Technical Support avr@atmel.com Sales Contact www.atmel.com/contacts Literature Requests www.atmel.com/literature Disclaimer: The information in this document is provided in connection with Atmel products. No license, express or implied, by estoppel or otherwise, to any intellectual property right is granted by this document or in connection with the sale of Atmel products. EXCEPT AS SET FORTH IN ATMEL'S TERMS AND CONDITIONS OF SALE LOCATED ON ATMEL'S WEB SITE, ATMEL ASSUMES NO LIABILITY WHATSOEVER AND DISCLAIMS ANY EXPRESS, IMPLIED OR STATUTORY WARRANTY RELATING TO ITS PRODUCTS INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT. IN NO EVENT SHALL ATMEL BE LIABLE FOR ANY DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE, SPECIAL OR INCIDENTAL DAMAGES (INCLUDING, WITHOUT LIMITATION, DAMAGES FOR LOSS OF PROFITS, BUSINESS INTERRUPTION, OR LOSS OF INFORMATION) ARISING OUT OF THE USE OR INABILITY TO USE THIS DOCUMENT, EVEN IF ATMEL HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. Atmel makes no representations or warranties with respect to the accuracy or completeness of the contents of this document and reserves the right to make changes to specifications and product descriptions at any time without notice. Atmel does not make any commitment to update the information contained herein. Unless specifically provided otherwise, Atmel products are not suitable for, and shall not be used in, automotive applications. Atmel's products are not intended, authorized, or warranted for use as components in applications intended to support or sustain life. (c) 2009 Atmel Corporation. All rights reserved. Atmel(R), logo and combinations thereof, AVR (R), AVR Studio (R) and others are registered trademarks or trademarks of Atmel Corporation or its subsidiaries. Other terms and product names may be trademarks of others. 7753C-AVR-07/09 |
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